adminui: an admin interface, behind authentication without exception

Replaces the unauthenticated admin mux. Everything but /healthz requires a
session, and that is the point: the previous arrangement relied on binding to
loopback, which worked exactly until the address changed and then failed
silently and publicly. A binding address is a deployment detail, not an access
control, and this package does not treat it as one.

Two ways in. OIDC through the confidential client, with state and PKCE - PKCE
even here, because it costs one hash and closes code interception independently
of the secret. And the break-glass password, throttled, for when the IdP is the
thing that is broken. Signing in without the admin group is refused with the
group named, because "you are not an admin" is a different problem from "your
password is wrong" and the remedy is elsewhere.

Sessions are MAC-checked cookies: HttpOnly, SameSite=Lax, Secure when TLS is on.
CSRF tokens are derived from the session rather than stored, so there is no
server-side table to keep in sync, and they are required on every state-changing
POST - SameSite already blocks cross-site posts in current browsers, but this is
the control that does not depend on the browser being current.

Server-rendered with html/template and no JavaScript: the pages are lists and
forms, and a framework would add a build step, a dependency tree and an update
treadmill to a program that has none of those. The CSP is default-src 'none'
accordingly.

Pages: overview, devices (with revocation and enrolment-link minting), uploaded
runs and a run viewer. Revocations and deletions are logged with who did them.
Runs are shown exactly as uploaded, at the privacy level their uploader chose -
nothing in the UI can un-redact one.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/build-status.md

@@ -1002,3 +1002,55 @@ Also fixed: the Settings *Preview what an upload would send* button did nothing.
 `UiState.history`, which is empty until the History screen has been opened — the same root cause as
 the "0 run(s)" count. It now reads the archive directly, and says so when there is nothing to
 preview rather than silently ignoring the tap.
+
+### Security: the admin listener was publicly exposed for ~15 minutes (2026-08-01)
+Moving the admin listener to `[::2]:443` for the UI exposed `/admin/enroll-tokens` and
+`/admin/selftest` to the internet **with no authentication**. Anyone who could reach
+`fmr.echo-lot.app` could mint enrolment tokens.
+
+The listener was designed localhost-only — its own flag help says *"keep localhost"* — and that
+assumption travelled with it when the address changed. The compounding error: `checkAdminExposure`,
+added the same day, verifies **encryption** and says nothing about **authentication**. It passed,
+and a green light on an adjacent property is worse than no check, because it invites you to stop
+looking.
+
+Closed by returning to loopback (the TLS and ACME work is retained, just not exposed). All 68 device
+enrolments matched the timestamps of test runs, so there is no evidence of abuse — but the window
+existed on a freshly published hostname and absence cannot be proven. 39 unused enrolment tokens
+were purged, since any could have been minted by someone else and they cost nothing to replace, and
+63 test devices removed.
+
+**The admin listener does not become reachable again until it authenticates.** That reorders the UI
+work: auth on the listener first, everything else after.
+
+### Open: encrypted uploads, where the operator cannot read the data
+Not built. Recorded because the shape is decided by a few early choices, and the current design
+happens to leave the door open.
+
+The goal: hand someone an account, let them upload, and be unable to read what they uploaded.
+
+Sketch: a random per-account **master key**, generated on the first device and wrapped under a
+key derived from a passphrase (PBKDF2-HMAC-SHA256 — stdlib on both sides). The wrapped key is
+stored server-side as an opaque blob, so a new device signs in, fetches it, and unwraps locally;
+the server never sees either key. Runs are encrypted client-side with AES-256-GCM, fresh nonce per
+run. All of this is stdlib in Go and `javax.crypto` in Kotlin — no dependency either side.
+
+Four consequences that decide whether it is worth it:
+
+1. **What stays readable determines what the UI can do.** The server builds its index by *parsing*
+   the document — verdict, finding count, started_at. An opaque payload means the client supplies
+   that metadata or the index disappears, and with it retention-by-verdict and any "runs with
+   findings" view. The honest version supplies only run id, timestamp and size, and moves the rest
+   client-side.
+2. **Lose the passphrase, lose the data.** That is the feature working, and also the support
+   burden. It needs a recovery code printed at setup, not a reset flow — there is nothing to reset.
+3. **Metadata is not hidden.** The operator still sees which account uploaded, when, how often and
+   how large. "Cannot see it" is about content, not existence, and saying otherwise would oversell.
+4. **It makes `min_anonymization` unenforceable** — a server cannot check a level it cannot read.
+   That is not a conflict so much as a redundancy: the anonymization floor exists to protect the
+   user from the operator, and encryption does that better. The two should not both be demanded of
+   one upload.
+
+What keeps this possible: uploads are already stored byte-for-byte as received, and every index
+field is derived in one function (`runs.Put`). The thing to avoid is admin features that *require*
+reading content — those would have to be unbuilt later.

server/Dockerfile

@@ -22,4 +22,7 @@ VOLUME ["/state"]
 # the data plane must see real client source addresses/TTLs, and Docker's
 # userland NAT would falsify exactly what this server exists to observe.
 EXPOSE 8441/tcp 8442/udp 8443/tcp
+# The verb is explicit here too, so `docker run <image>` serves and `docker run <image> --help`
+# still works by overriding the command.
 ENTRYPOINT ["/echolot-server"]
+CMD ["--serve"]

server/README.md

@@ -146,3 +146,41 @@ CI (`.gitea/workflows/build-server.yml`): tests on every push touching `server/`
 tagging `server-v1.2.3` builds + pushes the container image to the Gitea registry and
 attaches static linux amd64/arm64 binaries (+ SHA256SUMS) to a release — the same
 artifacts `--self-update` consumes.
+
+## TLS for the admin UI
+
+The binary terminates TLS itself; there is no reverse proxy in the design. It already serves TLS
+for the control plane, so this is reuse rather than new machinery, and it keeps the "one process,
+one config file" property. A proxy would also invite someone to eventually front the control plane
+too — which would break SPKI pinning, because clients pin *that* certificate's key.
+
+```
+ECHOLOT_ADMIN_LISTEN=[2001:db8::2]:443
+ECHOLOT_ADMIN_TLS_CERT=/etc/echolot/admin.pem
+ECHOLOT_ADMIN_TLS_KEY=/etc/echolot/admin.key
+ECHOLOT_ADMIN_BASE_URL=https://admin.example.net
+```
+
+Certificates come from any ACME client. **DNS-01 is the one to use here**: it needs no inbound
+port 80, which matters on a host where 80 is awkward or already spoken for.
+
+```sh
+acme.sh --issue --dns dns_cf -d admin.example.net \
+  --key-file       /etc/echolot/admin.key \
+  --fullchain-file /etc/echolot/admin.pem
+```
+
+**No reload hook is needed.** The certificate is re-read when the files change, so a renewal that
+drops new files in place is picked up on the next handshake. That is deliberate: a reload hook is
+the part of a renewal setup that quietly stops working, months later, and is noticed only once the
+certificate has already expired. A torn write — renewal tools write cert and key separately — keeps
+the previous certificate rather than failing the listener.
+
+Serving the admin UI in plaintext on a non-loopback address is refused: the session cookie is a
+bearer credential for everything the server can do, and the OIDC authorization code arrives in a
+URL. Bind to loopback and use an SSH tunnel (`ssh -L 8444:localhost:8444 host`), supply a
+certificate, or set `ECHOLOT_ADMIN_INSECURE=1` if you mean it.
+
+The control-plane certificate is deliberately *not* hot-reloaded. Clients pin its public key, so
+replacing it is a rotation an operator should have to think about, not something that happens
+because a file changed.

server/cmd/echolot-server/main.go

@@ -11,6 +11,7 @@
 package main
 
 import (
+	"bufio"
 	"context"
 	"crypto/ecdsa"
 	"crypto/elliptic"
@@ -18,7 +19,6 @@ import (
 	"crypto/tls"
 	"crypto/x509"
 	"crypto/x509/pkix"
-	"encoding/json"
 	"encoding/pem"
 	"errors"
 	"fmt"
@@ -36,7 +36,11 @@ import (
 	"syscall"
 	"time"
 
+	"echo-lot.app/server/internal/acmehttp"
+	"echo-lot.app/server/internal/adminauth"
+	"echo-lot.app/server/internal/adminui"
 	"echo-lot.app/server/internal/canarydns"
+	"echo-lot.app/server/internal/certreload"
 	"echo-lot.app/server/internal/compat"
 	"echo-lot.app/server/internal/config"
 	"echo-lot.app/server/internal/control"
@@ -70,6 +74,30 @@ func run() error {
 	control.Version = Version
 
 	switch {
+	case actions.Help:
+		// Compatibility shim for one release.
+		//
+		// Serving became an explicit verb, but self-update is run by the *old* binary — so the
+		// repair added to the updater cannot fix the very update that installs the new one. A
+		// unit written before this change starts us with no arguments, and without this branch
+		// the service would simply stop working, unattended, on a host nobody is watching.
+		//
+		// Only when systemd started us: INVOCATION_ID is set by systemd for every service
+		// invocation and by nothing else, so a person at a terminal still gets usage. Remove
+		// this once no deployment predates --serve.
+		if os.Getenv("INVOCATION_ID") != "" {
+			slog.Warn("started by systemd with no verb — this unit predates --serve; " +
+				"repairing it and serving anyway")
+			if repaired, err := system.RepairExecStart(); err != nil {
+				slog.Error("could not repair the unit; fix ExecStart by hand", "err", err)
+			} else if repaired {
+				slog.Info("systemd unit updated to pass --serve")
+			}
+			return serve(cfg)
+		}
+		config.Usage(os.Stderr)
+		os.Exit(2)
+		return nil
 	case actions.Version:
 		fmt.Println(Version)
 		return nil
@@ -80,6 +108,8 @@ func run() error {
 		return system.InstallSystemd(cfg.SelfUpdateAPI)
 	case actions.UninstallSystemd:
 		return system.UninstallSystemd()
+	case actions.SetAdminPassword:
+		return setAdminPassword(cfg)
 	case actions.SelfUpdate:
 		return selfupdate.Run(cfg.SelfUpdateAPI, Version)
 	}
@@ -154,20 +184,33 @@ func serve(cfg *config.Config) error {
 	// Identity is optional. Without an issuer the server simply has no sign-in, and
 	// uploads=account can never be satisfied — which is the honest outcome, not a silent
 	// downgrade to anonymous.
-	var idp *oidc.Verifier
+	// One verifier per issuer. An IdP may mint a distinct issuer per application — Authentik
-	if cfg.OIDCIssuer != "" && cfg.OIDCClientID != "" {
+	// derives it from the application slug — and a token's `iss` must match whoever signed it.
+	// Each verifier accepts only the client belonging to its own issuer, so a token minted for
+	// the phone cannot be replayed at the admin login and vice versa.
+	var idp, adminIdP *oidc.Verifier
+	appIssuer := cfg.OIDCAppIssuer
+	if appIssuer == "" {
+		appIssuer = cfg.OIDCIssuer // IdPs with one global issuer
+	}
+	if appIssuer != "" && cfg.OIDCAppClientID != "" {
 		idp = oidc.New(oidc.Config{
-			Issuer:     cfg.OIDCIssuer,
+			Issuer: appIssuer, AppClientID: cfg.OIDCAppClientID, AdminGroup: cfg.OIDCAdminGroup,
-			ClientID:   cfg.OIDCClientID,
-			AdminGroup: cfg.OIDCAdminGroup,
 		}, nil)
-		slog.Info("identity provider configured", "issuer", cfg.OIDCIssuer,
+		slog.Info("identity: app client", "issuer", appIssuer, "client_id", cfg.OIDCAppClientID)
+	}
+	if cfg.OIDCIssuer != "" && cfg.OIDCClientID != "" {
+		adminIdP = oidc.New(oidc.Config{
+			Issuer: cfg.OIDCIssuer, ClientID: cfg.OIDCClientID, AdminGroup: cfg.OIDCAdminGroup,
+		}, nil)
+		slog.Info("identity: admin client", "issuer", cfg.OIDCIssuer,
 			"client_id", cfg.OIDCClientID, "admin_group", cfg.OIDCAdminGroup)
 		if cfg.OIDCAdminGroup == "" {
 			slog.Warn("no admin group set: nobody will be an admin via OIDC " +
 				"(set ECHOLOT_OIDC_ADMIN_GROUP)")
 		}
-	} else if cfg.UploadsMode == string(runs.ModeAccount) {
+	}
+	if idp == nil && adminIdP == nil && cfg.UploadsMode == string(runs.ModeAccount) {
 		slog.Warn("uploads=account but no identity provider is configured — " +
 			"every upload will be refused")
 	}
@@ -184,6 +227,7 @@ func serve(cfg *config.Config) error {
 		AppRange:         appRange,
 		PublicControlURL: publicControlURL(cfg),
 		OIDC:             idp,
+		AdminOIDC:        adminIdP,
 	}
 	// Left nil when there is no raw socket, so the handler answers "not implemented" with a
 	// reason rather than failing somewhere deeper.
@@ -253,38 +297,76 @@ func serve(cfg *config.Config) error {
 		return best
 	}
 
-	// Admin/health (plain HTTP, localhost by default; spec §7)
+	// The admin interface. Every route except /healthz requires a session — the old arrangement
-	admin := http.NewServeMux()
+	// (no auth, kept safe by binding to loopback) failed the moment the address changed, and a
-	admin.HandleFunc("GET /healthz", func(w http.ResponseWriter, _ *http.Request) {
+	// binding address is a deployment detail rather than an access control.
-		fmt.Fprintf(w, `{"ok":true,"version":%q}`, Version)
+	secret, err := st.SessionSecret()
-	})
-	admin.HandleFunc("GET /admin/selftest", func(w http.ResponseWriter, _ *http.Request) {
-		w.Header().Set("Content-Type", "application/json")
-		_ = json.NewEncoder(w).Encode(selftestPtr.Load())
-	})
-	// TODO(spec §7): enrollment token management + device list. Until the
-	// admin UI exists, mint tokens with: echolot-admin (or curl on this
-	// listener once the endpoint lands).
-	admin.HandleFunc("POST /admin/enroll-tokens", func(w http.ResponseWriter, r *http.Request) {
-		tok, err := st.NewEnrollToken(24*time.Hour, r.URL.Query().Get("note"))
 	if err != nil {
-			http.Error(w, err.Error(), 500)
+		return fmt.Errorf("admin session secret: %w", err)
-			return
 	}
-		// The whole bootstrap, not just the token: this is what gets pasted or turned into a
+	adminSecure := cfg.AdminTLSCert != ""
-		// QR code, and assembling it here is what keeps an operator from transcribing a pin by
+	ui := &adminui.Server{
-		// hand — a pin wrong by one character fails as an inscrutable TLS error days later.
+		Store:        st,
-		w.Header().Set("Content-Type", "application/json")
+		Runs:         runStore,
-		enc := json.NewEncoder(w)
+		OIDC:         adminIdP,
-		enc.SetEscapeHTML(false) // the link is full of / and =; escaping them helps nobody
+		Sessions:     adminauth.NewSessions(secret, 12*time.Hour),
-		_ = enc.Encode(map[string]any{
+		Throttle:     adminauth.NewThrottle(),
-			"token":        tok,
+		AdminUser:    cfg.AdminUser,
-			"expires_in_s": 86400,
+		BaseURL:      cfg.AdminBaseURL,
-			"enroll_uri":   ctl.EnrollmentLink(tok),
+		ClientSecret: cfg.OIDCClientSecret,
-		})
+		Secure:       adminSecure,
-	})
+		EnrollLink:   ctl.EnrollmentLink,
+		SelfTest:     func() any { return selftestPtr.Load() },
+		Version:      Version,
+	}
+	if st.LocalAdmin() == nil && adminIdP == nil {
+		slog.Warn("nobody can sign in to the admin UI: no break-glass password is set " +
+			"(--set-admin-password) and no identity provider is configured")
+	}
+	admin := ui.Handler()
+
 	adminSrv := &http.Server{Addr: cfg.AdminListen, Handler: admin, ReadHeaderTimeout: 10 * time.Second}
+	if cfg.AdminTLSCert != "" {
+		// Terminated here rather than behind a reverse proxy: this binary already serves TLS for
+		// the control plane, so it is reuse rather than new machinery, and one process with one
+		// config file is the property that makes this pleasant to run. A proxy would also invite
+		// someone to later front the control plane too, which would break SPKI pinning.
+		reloader, err := certreload.New(cfg.AdminTLSCert, cfg.AdminTLSKey)
+		if err != nil {
+			return fmt.Errorf("admin TLS: %w", err)
+		}
+		adminSrv.TLSConfig = reloader.TLSConfig()
+		if exp := reloader.NotAfter(); !exp.IsZero() {
+			slog.Info("admin UI TLS", "listen", cfg.AdminListen, "cert_expires", exp.Format(time.RFC3339))
+			if time.Until(exp) < 14*24*time.Hour {
+				slog.Warn("admin certificate expires soon", "expires", exp.Format(time.RFC3339))
+			}
+		}
+		go func() { errCh <- fmt.Errorf("admin: %w", adminSrv.ListenAndServeTLS("", "")) }()
+	} else {
 		go func() { errCh <- fmt.Errorf("admin: %w", adminSrv.ListenAndServe()) }()
+	}
+
+	// ACME HTTP-01 responder. Permanent rather than started per renewal: nothing binds and
+	// unbinds, so a renewal cannot fail because the port was briefly busy, and the ACME client
+	// needs only write access to a directory instead of the privilege to bind a low port.
+	if cfg.ACMEHTTPListen != "" {
+		webroot := cfg.ACMEWebroot
+		if webroot == "" {
+			webroot = filepath.Join(cfg.StateDir, "acme")
+		}
+		if err := acmehttp.EnsureWebroot(webroot); err != nil {
+			return fmt.Errorf("acme webroot: %w", err)
+		}
+		acmeSrv := &http.Server{
+			Addr:              cfg.ACMEHTTPListen,
+			Handler:           acmehttp.Handler(webroot, cfg.AdminBaseURL),
+			ReadHeaderTimeout: 10 * time.Second,
+		}
+		slog.Info("acme http-01 responder", "listen", cfg.ACMEHTTPListen, "webroot", webroot,
+			"redirects_to", cfg.AdminBaseURL)
+		go func() { errCh <- fmt.Errorf("acme-http: %w", acmeSrv.ListenAndServe()) }()
+	}
 
 	// UDP data plane — one socket per configured address. Distinct sockets
 	// (not wildcard) also guarantee responses leave from the address the
@@ -516,3 +598,48 @@ func publicControlURL(cfg *config.Config) string {
 	}
 	return "https://" + addr
 }
+
+// setAdminPassword stores the break-glass admin credential.
+//
+// The password is read from stdin rather than taken as a flag, so it never lands in shell
+// history, in the process list where any local user can see it, or in a systemd unit. Piping is
+// still possible for automation:
+//
+//	printf '%s' "$PW" | echolot-server --set-admin-password --admin-user ops
+func setAdminPassword(cfg *config.Config) error {
+	st, err := store.Open(cfg.StateDir)
+	if err != nil {
+		return fmt.Errorf("state store: %w", err)
+	}
+	fmt.Fprintf(os.Stderr, "New password for %q (input is not echoed if this is a terminal): ", cfg.AdminUser)
+	pw, err := readSecret()
+	if err != nil {
+		return err
+	}
+	fmt.Fprintln(os.Stderr)
+
+	cred, err := adminauth.NewCredential(cfg.AdminUser, pw)
+	if err != nil {
+		return err
+	}
+	if err := st.SetLocalAdmin(cred); err != nil {
+		return err
+	}
+	fmt.Fprintf(os.Stderr, "Break-glass admin %q set. This account works even when the identity\n"+
+		"provider does not, which is the point of it — treat the password accordingly.\n", cfg.AdminUser)
+	return nil
+}
+
+// readSecret reads one line from stdin, without echo where the terminal allows it.
+func readSecret() (string, error) {
+	restore, _ := system.DisableEcho(os.Stdin)
+	if restore != nil {
+		defer restore()
+	}
+	r := bufio.NewReader(os.Stdin)
+	line, err := r.ReadString('\n')
+	if err != nil && line == "" {
+		return "", err
+	}
+	return strings.TrimSpace(line), nil
+}

server/internal/acmehttp/acmehttp.go

@@ -0,0 +1,100 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+// Package acmehttp answers ACME HTTP-01 challenges and sends everything else to HTTPS.
+//
+// HTTP-01 validation always arrives on port 80 — the CA chooses the port, not the operator — so
+// it never collides with an admin UI on 443. That leaves two ways to answer it: let the ACME
+// client bind port 80 for a few seconds during each renewal, or keep something there permanently
+// that serves the challenge directory. This is the second, and it is the better trade:
+//
+//   - nothing binds and unbinds, so renewal cannot fail because the port was briefly busy;
+//   - the ACME client needs no privileges to bind a low port, only write access to a directory;
+//   - port 80 gets a use it would want anyway, redirecting people who typed http:// to the real
+//     thing instead of hanging.
+//
+// It is the same arrangement as the webroot plugins for Apache and nginx, and it works with any
+// ACME client that can write a file: `lego --http.webroot`, `certbot --webroot`, `acme.sh -w`.
+//
+// The ACME client stays an external program on purpose. lego is also a Go library, but importing
+// it would put a large dependency tree into a server that deliberately has none — and the CLI does
+// the same job from a timer.
+package acmehttp
+
+import (
+	"log/slog"
+	"net/http"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+// ChallengePath is the fixed prefix ACME uses. It is not configurable, by the specification.
+const ChallengePath = "/.well-known/acme-challenge/"
+
+// Handler serves challenge tokens from webroot and redirects everything else to redirectTo.
+//
+// webroot is the directory an ACME client writes into; the tokens themselves land in
+// <webroot>/.well-known/acme-challenge/<token>, which is exactly what --http.webroot expects.
+func Handler(webroot, redirectTo string) http.Handler {
+	mux := http.NewServeMux()
+
+	mux.HandleFunc(ChallengePath, func(w http.ResponseWriter, r *http.Request) {
+		token := strings.TrimPrefix(r.URL.Path, ChallengePath)
+		// Tokens are base64url from the CA. Anything else is somebody probing, and refusing by
+		// shape means path traversal never gets as far as touching the filesystem.
+		if token == "" || !validToken(token) {
+			http.NotFound(w, r)
+			return
+		}
+		body, err := os.ReadFile(filepath.Join(webroot, filepath.FromSlash(ChallengePath), token))
+		if err != nil {
+			// Logged at info: a challenge that cannot be answered is why a renewal failed, and
+			// that is worth being able to see afterwards rather than guessing at it.
+			slog.Info("acme challenge not found", "token", token, "webroot", webroot)
+			http.NotFound(w, r)
+			return
+		}
+		slog.Info("answered acme challenge", "token", token, "from", r.RemoteAddr)
+		w.Header().Set("Content-Type", "text/plain")
+		_, _ = w.Write(body)
+	})
+
+	mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
+		if redirectTo == "" {
+			http.Error(w, "this port serves ACME challenges only", http.StatusNotFound)
+			return
+		}
+		// 308 rather than 302: the method must not change, and the redirect is permanent in the
+		// sense that matters — this port will never serve the application.
+		http.Redirect(w, r, strings.TrimRight(redirectTo, "/")+r.URL.RequestURI(), http.StatusPermanentRedirect)
+	})
+
+	return mux
+}
+
+// validToken accepts only the base64url alphabet the ACME spec uses for tokens.
+//
+// A shape check rather than a path check: "../../etc/shadow" fails here before any filesystem
+// call, which is a stronger guarantee than sanitising a path and hoping the sanitiser is right.
+func validToken(s string) bool {
+	if len(s) > 128 {
+		return false
+	}
+	for _, r := range s {
+		switch {
+		case r >= 'a' && r <= 'z', r >= 'A' && r <= 'Z', r >= '0' && r <= '9', r == '-', r == '_', r == '.':
+		default:
+			return false
+		}
+	}
+	// A bare "." or ".." never appears in a real token and is the one traversal the alphabet
+	// above would otherwise permit.
+	return s != "." && s != ".."
+}
+
+// EnsureWebroot creates the challenge directory, so an ACME client's first run does not fail on a
+// missing path and an operator does not have to know the layout.
+func EnsureWebroot(webroot string) error {
+	return os.MkdirAll(filepath.Join(webroot, filepath.FromSlash(ChallengePath)), 0o755)
+}

server/internal/acmehttp/acmehttp_test.go

@@ -0,0 +1,98 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package acmehttp
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func serve(t *testing.T, redirectTo string) (http.Handler, string) {
+	t.Helper()
+	root := t.TempDir()
+	if err := EnsureWebroot(root); err != nil {
+		t.Fatal(err)
+	}
+	return Handler(root, redirectTo), root
+}
+
+func TestServesAChallengeTokenWrittenByAnAcmeClient(t *testing.T) {
+	h, root := serve(t, "https://admin.example.net")
+	// Exactly what `lego --http.webroot` writes.
+	token := "abc-123_XYZ"
+	want := "abc-123_XYZ.keyauthorization-part"
+	if err := os.WriteFile(filepath.Join(root, ".well-known", "acme-challenge", token), []byte(want), 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	rec := httptest.NewRecorder()
+	h.ServeHTTP(rec, httptest.NewRequest("GET", ChallengePath+token, nil))
+	if rec.Code != 200 {
+		t.Fatalf("challenge not served: %d", rec.Code)
+	}
+	if rec.Body.String() != want {
+		t.Fatalf("body = %q, want %q", rec.Body.String(), want)
+	}
+}
+
+// The token comes from the network and is used to build a path. Rejecting by *shape* means
+// traversal never reaches the filesystem at all, which is a stronger guarantee than sanitising.
+func TestTraversalNeverTouchesTheFilesystem(t *testing.T) {
+	h, root := serve(t, "https://admin.example.net")
+	secret := filepath.Join(filepath.Dir(root), "secret.txt")
+	if err := os.WriteFile(secret, []byte("do not serve me"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	for _, bad := range []string{
+		"../secret.txt",
+		"..%2Fsecret.txt",
+		"../../etc/passwd",
+		"..",
+		".",
+		"a/b",
+		"tok%20en", // a space arrives percent-encoded; a literal one is not a valid request line
+	} {
+		rec := httptest.NewRecorder()
+		h.ServeHTTP(rec, httptest.NewRequest("GET", ChallengePath+bad, nil))
+		if rec.Code == 200 && rec.Body.String() == "do not serve me" {
+			t.Fatalf("served a file outside the challenge directory via %q", bad)
+		}
+	}
+}
+
+func TestEverythingElseRedirectsToHTTPS(t *testing.T) {
+	h, _ := serve(t, "https://admin.example.net")
+	rec := httptest.NewRecorder()
+	h.ServeHTTP(rec, httptest.NewRequest("GET", "/devices?page=2", nil))
+	if rec.Code != http.StatusPermanentRedirect {
+		t.Fatalf("code = %d, want 308", rec.Code)
+	}
+	// The path and query must survive, or a bookmarked link lands on the wrong page.
+	if got := rec.Header().Get("Location"); got != "https://admin.example.net/devices?page=2" {
+		t.Fatalf("Location = %q", got)
+	}
+}
+
+// With no admin URL configured there is nowhere to send people, and inventing one would be worse
+// than saying so.
+func TestNoRedirectTargetIsHonest(t *testing.T) {
+	h, _ := serve(t, "")
+	rec := httptest.NewRecorder()
+	h.ServeHTTP(rec, httptest.NewRequest("GET", "/", nil))
+	if rec.Code != http.StatusNotFound {
+		t.Fatalf("code = %d, want 404", rec.Code)
+	}
+}
+
+func TestMissingTokenIsNotFound(t *testing.T) {
+	h, _ := serve(t, "https://admin.example.net")
+	rec := httptest.NewRecorder()
+	h.ServeHTTP(rec, httptest.NewRequest("GET", ChallengePath+"never-written", nil))
+	if rec.Code != http.StatusNotFound {
+		t.Fatalf("code = %d, want 404", rec.Code)
+	}
+}

server/internal/adminauth/adminauth.go

@@ -0,0 +1,253 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+// Package adminauth handles who may administer the server.
+//
+// Two ways in, deliberately:
+//
+//   - **OIDC**, the normal one. Identity lives in the operator's own IdP.
+//   - **A local admin password**, the break-glass one. If the IdP is misconfigured, unreachable,
+//     or the operator fat-fingered the admin group, they would otherwise be locked out of their
+//     own server with no way back in short of editing JSON on disk. A fallback that only works
+//     when everything else is broken is exactly the thing you cannot add later, because by then
+//     you cannot get in to add it.
+//
+// The local password is stored as PBKDF2-HMAC-SHA256, from the standard library (Go 1.24+), with
+// a per-credential salt. Not because password login is encouraged — it is the fallback — but
+// because a break-glass credential is precisely the one most likely to end up in a backup or a
+// config-management repo, and a hash survives that where a bearer token does not.
+//
+// There is no email reset flow and there should not be: `--set-admin-password` on the host *is*
+// the reset, and anyone who can run it already has the machine.
+package adminauth
+
+import (
+	"crypto/hmac"
+	"crypto/pbkdf2"
+	"crypto/rand"
+	"crypto/sha256"
+	"crypto/subtle"
+	"encoding/base64"
+	"encoding/hex"
+	"errors"
+	"fmt"
+	"strconv"
+	"strings"
+	"sync"
+	"time"
+)
+
+// iterations follows OWASP's guidance for PBKDF2-HMAC-SHA256. Deliberately slow: this credential
+// is used a handful of times in a server's life, so the cost is invisible to the operator and
+// meaningful to anyone grinding a stolen hash.
+const iterations = 600_000
+
+const (
+	saltLen = 16
+	keyLen  = 32
+)
+
+// Credential is a stored local admin password.
+type Credential struct {
+	Username   string `json:"username"`
+	Salt       string `json:"salt"` // hex
+	Hash       string `json:"hash"` // hex
+	Iterations int    `json:"iterations"`
+	Updated    string `json:"updated,omitempty"`
+}
+
+// NewCredential derives a stored credential from a plaintext password.
+func NewCredential(username, password string) (Credential, error) {
+	if strings.TrimSpace(username) == "" {
+		return Credential{}, errors.New("username must not be empty")
+	}
+	// Twelve is not a policy so much as a floor: this is the one account that can reach
+	// everything, and it is not rate-limited by a human being's patience.
+	if len(password) < 12 {
+		return Credential{}, errors.New("password must be at least 12 characters")
+	}
+	salt := make([]byte, saltLen)
+	if _, err := rand.Read(salt); err != nil {
+		return Credential{}, err
+	}
+	key, err := pbkdf2.Key(sha256.New, password, salt, iterations, keyLen)
+	if err != nil {
+		return Credential{}, err
+	}
+	return Credential{
+		Username:   username,
+		Salt:       hex.EncodeToString(salt),
+		Hash:       hex.EncodeToString(key),
+		Iterations: iterations,
+		Updated:    time.Now().UTC().Format(time.RFC3339),
+	}, nil
+}
+
+// Verify checks a username and password against this credential.
+//
+// Both comparisons are constant-time, including the username: a fast rejection on an unknown
+// username is a timing oracle for which usernames exist. The stored iteration count is used
+// rather than the current constant, so raising the constant does not lock out existing passwords.
+func (c Credential) Verify(username, password string) bool {
+	if c.Username == "" || c.Hash == "" {
+		return false
+	}
+	salt, err := hex.DecodeString(c.Salt)
+	if err != nil {
+		return false
+	}
+	want, err := hex.DecodeString(c.Hash)
+	if err != nil {
+		return false
+	}
+	iter := c.Iterations
+	if iter <= 0 {
+		iter = iterations
+	}
+	got, err := pbkdf2.Key(sha256.New, password, salt, iter, len(want))
+	if err != nil {
+		return false
+	}
+	userOK := subtle.ConstantTimeCompare([]byte(c.Username), []byte(username)) == 1
+	passOK := subtle.ConstantTimeCompare(got, want) == 1
+	return userOK && passOK
+}
+
+// Throttle slows repeated failures against the local password.
+//
+// The local admin is a single well-known account guarding everything, so an unthrottled login
+// form is an offline-speed guessing oracle that happens to be online. This is deliberately crude
+// — a delay that grows with consecutive failures and resets on success — because the goal is to
+// make guessing impractical, not to build a lockout system that an operator can trap themselves
+// with. It never locks permanently: a break-glass credential that can be locked out by an
+// attacker is a denial of service against the person who needs it most.
+type Throttle struct {
+	mu       sync.Mutex
+	failures int
+	last     time.Time
+	now      func() time.Time
+}
+
+func NewThrottle() *Throttle { return &Throttle{now: time.Now} }
+
+// Delay is how long the caller should wait before answering, given the failures so far.
+func (t *Throttle) Delay() time.Duration {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	// A quiet minute forgives everything, so an operator returning later is not punished for
+	// somebody else's earlier attempts.
+	if !t.last.IsZero() && t.now().Sub(t.last) > time.Minute {
+		t.failures = 0
+	}
+	switch {
+	case t.failures == 0:
+		return 0
+	case t.failures < 3:
+		return 250 * time.Millisecond
+	case t.failures < 6:
+		return time.Second
+	default:
+		return 3 * time.Second
+	}
+}
+
+func (t *Throttle) Failed() {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	t.failures++
+	t.last = t.now()
+}
+
+func (t *Throttle) Succeeded() {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	t.failures = 0
+}
+
+// ---- sessions ---------------------------------------------------------------------------
+
+// Session is an authenticated admin, however they proved it.
+type Session struct {
+	// Subject is the account id: "local:<username>" or "<issuer>#<sub>" from OIDC.
+	Subject string
+	// Display is what the UI shows.
+	Display string
+	Expires time.Time
+}
+
+// Sessions mints and checks signed session cookies.
+//
+// The cookie carries its own contents and a MAC, so there is no server-side session table to
+// grow, expire, or lose on restart — and equally no way to revoke one early, which is why they
+// are short-lived. The secret is persisted, so an operator's session survives a service restart;
+// regenerating it (deleting it from the state file) invalidates every session at once, which is
+// the revocation mechanism.
+type Sessions struct {
+	secret []byte
+	ttl    time.Duration
+}
+
+func NewSessions(secret []byte, ttl time.Duration) *Sessions {
+	if ttl <= 0 {
+		ttl = 12 * time.Hour
+	}
+	return &Sessions{secret: append([]byte(nil), secret...), ttl: ttl}
+}
+
+// NewSecret makes a fresh signing secret for first start.
+func NewSecret() ([]byte, error) {
+	b := make([]byte, 32)
+	_, err := rand.Read(b)
+	return b, err
+}
+
+var ErrSession = errors.New("session is not valid")
+
+// Issue returns the cookie value for a newly authenticated admin.
+func (s *Sessions) Issue(subject, display string) string {
+	exp := time.Now().Add(s.ttl).Unix()
+	payload := base64.RawURLEncoding.EncodeToString([]byte(subject)) + "." +
+		base64.RawURLEncoding.EncodeToString([]byte(display)) + "." +
+		strconv.FormatInt(exp, 10)
+	return payload + "." + s.mac(payload)
+}
+
+// Parse checks a cookie value and returns the session it encodes.
+func (s *Sessions) Parse(value string) (*Session, error) {
+	i := strings.LastIndex(value, ".")
+	if i < 0 {
+		return nil, ErrSession
+	}
+	payload, sig := value[:i], value[i+1:]
+	// MAC first, always. Nothing in the payload is believed — not even its shape — before the
+	// signature has been checked.
+	if !hmac.Equal([]byte(sig), []byte(s.mac(payload))) {
+		return nil, ErrSession
+	}
+	parts := strings.Split(payload, ".")
+	if len(parts) != 3 {
+		return nil, ErrSession
+	}
+	subject, err := base64.RawURLEncoding.DecodeString(parts[0])
+	if err != nil {
+		return nil, ErrSession
+	}
+	display, err := base64.RawURLEncoding.DecodeString(parts[1])
+	if err != nil {
+		return nil, ErrSession
+	}
+	exp, err := strconv.ParseInt(parts[2], 10, 64)
+	if err != nil {
+		return nil, ErrSession
+	}
+	if time.Now().After(time.Unix(exp, 0)) {
+		return nil, fmt.Errorf("%w: expired", ErrSession)
+	}
+	return &Session{Subject: string(subject), Display: string(display), Expires: time.Unix(exp, 0)}, nil
+}
+
+func (s *Sessions) mac(payload string) string {
+	m := hmac.New(sha256.New, s.secret)
+	m.Write([]byte(payload))
+	return base64.RawURLEncoding.EncodeToString(m.Sum(nil))
+}

server/internal/adminauth/adminauth_test.go

@@ -0,0 +1,203 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package adminauth
+
+import (
+	"strings"
+	"testing"
+	"time"
+)
+
+// PBKDF2 at 600k iterations is slow on purpose, so these use a reduced count where the test is
+// about logic rather than cost.
+func fastCredential(t *testing.T, user, pass string) Credential {
+	t.Helper()
+	c, err := NewCredential(user, pass)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return c
+}
+
+func TestVerifyAcceptsOnlyTheRightPair(t *testing.T) {
+	c := fastCredential(t, "admin", "correct-horse-battery")
+
+	if !c.Verify("admin", "correct-horse-battery") {
+		t.Fatal("the correct credentials were rejected")
+	}
+	for _, tc := range []struct{ user, pass string }{
+		{"admin", "wrong-password-here"},
+		{"admin", ""},
+		{"root", "correct-horse-battery"},
+		{"", "correct-horse-battery"},
+		{"ADMIN", "correct-horse-battery"}, // usernames are not case-folded
+	} {
+		if c.Verify(tc.user, tc.pass) {
+			t.Errorf("accepted %q/%q", tc.user, tc.pass)
+		}
+	}
+}
+
+// Two credentials with the same password must not share a hash, or one cracked password reveals
+// every reuse of it and a precomputed table works against all of them.
+func TestSaltsDiffer(t *testing.T) {
+	a := fastCredential(t, "admin", "the-same-password-x")
+	b := fastCredential(t, "admin", "the-same-password-x")
+	if a.Salt == b.Salt {
+		t.Fatal("two credentials share a salt")
+	}
+	if a.Hash == b.Hash {
+		t.Fatal("the same password produced the same hash twice")
+	}
+	// Both must still verify — a salt that is not actually used would also produce differing
+	// hashes if it were mixed in wrongly.
+	if !a.Verify("admin", "the-same-password-x") || !b.Verify("admin", "the-same-password-x") {
+		t.Fatal("a salted credential does not verify")
+	}
+}
+
+// The stored iteration count is used rather than the current constant, so raising the constant
+// later does not silently lock out every existing password.
+func TestOldIterationCountsStillVerify(t *testing.T) {
+	c := fastCredential(t, "admin", "a-perfectly-fine-pw")
+	c.Iterations = iterations // as stored
+	if !c.Verify("admin", "a-perfectly-fine-pw") {
+		t.Fatal("credential does not verify with its stored iteration count")
+	}
+	// A credential written before the field existed must not be treated as zero-iteration.
+	c.Iterations = 0
+	if !c.Verify("admin", "a-perfectly-fine-pw") {
+		t.Fatal("a credential with no recorded iteration count failed to verify")
+	}
+}
+
+func TestWeakInputsAreRefusedAtCreation(t *testing.T) {
+	if _, err := NewCredential("", "long-enough-password"); err == nil {
+		t.Error("an empty username was accepted")
+	}
+	if _, err := NewCredential("admin", "short"); err == nil {
+		t.Error("a short password was accepted")
+	}
+}
+
+func TestAnEmptyCredentialNeverVerifies(t *testing.T) {
+	var zero Credential
+	if zero.Verify("", "") {
+		t.Fatal("a server with no local admin configured accepted empty credentials")
+	}
+	if zero.Verify("admin", "anything") {
+		t.Fatal("an unset credential verified")
+	}
+}
+
+// ---- sessions ----------------------------------------------------------------------------
+
+func TestSessionRoundTrip(t *testing.T) {
+	secret, _ := NewSecret()
+	s := NewSessions(secret, time.Hour)
+	got, err := s.Parse(s.Issue("local:admin", "Admin"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got.Subject != "local:admin" || got.Display != "Admin" {
+		t.Fatalf("session did not round-trip: %+v", got)
+	}
+}
+
+// The cookie carries its own contents, so the MAC is the only thing standing between a user and
+// promoting themselves. Every tampered form must fail.
+func TestTamperedSessionsAreRejected(t *testing.T) {
+	secret, _ := NewSecret()
+	s := NewSessions(secret, time.Hour)
+	good := s.Issue("local:admin", "Admin")
+
+	parts := strings.Split(good, ".")
+	tampered := []string{
+		"",
+		"garbage",
+		good + "x", // signature altered
+		strings.Replace(good, parts[0], "Zm9v", 1), // subject swapped
+		strings.Join(parts[:len(parts)-1], "."),    // signature removed
+		parts[0] + "." + parts[1] + "." + parts[2], // signature removed, well-formed payload
+	}
+	for _, v := range tampered {
+		if _, err := s.Parse(v); err == nil {
+			t.Errorf("accepted a tampered session: %q", v)
+		}
+	}
+}
+
+func TestSessionsFromAnotherSecretAreRejected(t *testing.T) {
+	a, _ := NewSecret()
+	b, _ := NewSecret()
+	issued := NewSessions(a, time.Hour).Issue("local:admin", "Admin")
+	if _, err := NewSessions(b, time.Hour).Parse(issued); err == nil {
+		t.Fatal("a session signed with a different secret was accepted — rotating the secret " +
+			"must invalidate every existing session")
+	}
+}
+
+func TestExpiredSessionsAreRejected(t *testing.T) {
+	secret, _ := NewSecret()
+	// A negative TTL is not reachable through NewSessions, so issue with a real one and check
+	// the boundary via a session that has already run out.
+	s := NewSessions(secret, time.Millisecond)
+	v := s.Issue("local:admin", "Admin")
+	time.Sleep(10 * time.Millisecond)
+	if _, err := s.Parse(v); err == nil {
+		t.Fatal("an expired session was accepted")
+	}
+}
+
+// ---- throttle ------------------------------------------------------------------------------
+
+func TestThrottleGrowsWithFailuresAndResetsOnSuccess(t *testing.T) {
+	tr := NewThrottle()
+	if d := tr.Delay(); d != 0 {
+		t.Fatalf("a first attempt was delayed by %v", d)
+	}
+	for i := 0; i < 2; i++ {
+		tr.Failed()
+	}
+	first := tr.Delay()
+	for i := 0; i < 6; i++ {
+		tr.Failed()
+	}
+	later := tr.Delay()
+	if !(later > first && first > 0) {
+		t.Fatalf("delay did not grow with failures: %v then %v", first, later)
+	}
+	tr.Succeeded()
+	if d := tr.Delay(); d != 0 {
+		t.Fatalf("a successful login did not clear the throttle: %v", d)
+	}
+}
+
+// A break-glass credential that an attacker can lock out is a denial of service against the one
+// person who needs it. The delay must stay bounded rather than becoming a lockout.
+func TestThrottleNeverLocksOutPermanently(t *testing.T) {
+	tr := NewThrottle()
+	for i := 0; i < 1000; i++ {
+		tr.Failed()
+	}
+	if d := tr.Delay(); d > 10*time.Second {
+		t.Fatalf("throttle became a lockout: %v", d)
+	}
+}
+
+func TestThrottleForgivesAfterAQuietPeriod(t *testing.T) {
+	tr := NewThrottle()
+	now := time.Now()
+	tr.now = func() time.Time { return now }
+	for i := 0; i < 10; i++ {
+		tr.Failed()
+	}
+	if tr.Delay() == 0 {
+		t.Fatal("failures did not register")
+	}
+	now = now.Add(2 * time.Minute)
+	if d := tr.Delay(); d != 0 {
+		t.Fatalf("an operator returning later was still throttled: %v", d)
+	}
+}

server/internal/adminui/auth.go

@@ -0,0 +1,346 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+// Package adminui serves the operator's web interface.
+//
+// Everything here is behind authentication, without exception. The previous arrangement — an
+// unauthenticated listener kept safe by binding to loopback — worked exactly until the address
+// changed, and then failed silently and publicly. Binding address is a deployment detail; it is
+// not an access control, and this package does not treat it as one.
+//
+// Rendered server-side with html/template and no JavaScript. The pages are lists and forms; a
+// framework would add a build step, a dependency tree and an update treadmill to a program that
+// currently has none of those.
+package adminui
+
+import (
+	"context"
+	"crypto/rand"
+	"crypto/sha256"
+	"encoding/base64"
+	"encoding/json"
+	"fmt"
+	"io"
+	"log/slog"
+	"net/http"
+	"net/url"
+	"strings"
+	"time"
+
+	"echo-lot.app/server/internal/adminauth"
+	"echo-lot.app/server/internal/oidc"
+	"echo-lot.app/server/internal/runs"
+	"echo-lot.app/server/internal/store"
+)
+
+const (
+	sessionCookie = "echolot_admin"
+	stateCookie   = "echolot_oidc"
+	csrfField     = "csrf"
+)
+
+// Server is the admin interface.
+type Server struct {
+	Store    *store.Store
+	Runs     *runs.Store
+	OIDC     *oidc.Verifier // admin client; nil when no IdP is configured
+	Sessions *adminauth.Sessions
+	Throttle *adminauth.Throttle
+
+	// AdminUser is the break-glass username; the password hash lives in the store.
+	AdminUser string
+	// BaseURL is where this UI is reachable, for building the OIDC redirect. Must match the URI
+	// registered at the IdP exactly.
+	BaseURL string
+	// ClientSecret authenticates the confidential admin client at the token endpoint.
+	ClientSecret string
+	// Secure marks cookies Secure. Off only for loopback HTTP, where there is no network to
+	// intercept and browsers refuse Secure cookies over plaintext anyway.
+	Secure bool
+
+	// EnrollLink builds the §2.1 bootstrap link for a token. Injected rather than rebuilt here,
+	// so the SPKI pin and public URL stay owned by the control server that actually knows them.
+	EnrollLink func(token string) string
+	// SelfTest and Version render on the dashboard.
+	SelfTest func() any
+	Version  string
+}
+
+// Handler builds the routes. Only /healthz is reachable without a session.
+func (s *Server) Handler() http.Handler {
+	mux := http.NewServeMux()
+
+	// Unauthenticated: a health check that required a session would be no use to a monitor, and
+	// it discloses nothing beyond "the process is up".
+	mux.HandleFunc("GET /healthz", func(w http.ResponseWriter, _ *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		fmt.Fprintf(w, `{"ok":true,"version":%q}`+"\n", s.Version)
+	})
+
+	mux.HandleFunc("GET /login", s.loginForm)
+	mux.HandleFunc("POST /login", s.loginSubmit)
+	mux.HandleFunc("GET /auth/start", s.oidcStart)
+	mux.HandleFunc("GET /admin/callback", s.oidcCallback)
+	mux.HandleFunc("POST /logout", s.logout)
+
+	mux.HandleFunc("GET /", s.guard(s.dashboard))
+	mux.HandleFunc("GET /devices", s.guard(s.devices))
+	mux.HandleFunc("POST /devices/{id}/revoke", s.guard(s.revokeDevice))
+	mux.HandleFunc("POST /enroll-tokens", s.guard(s.mintToken))
+	mux.HandleFunc("GET /runs", s.guard(s.runsList))
+	mux.HandleFunc("GET /runs/{device}/{id}", s.guard(s.runView))
+	mux.HandleFunc("POST /runs/{device}/{id}/delete", s.guard(s.runDelete))
+
+	return mux
+}
+
+// guard requires a valid session, and checks CSRF on anything that changes state.
+func (s *Server) guard(h func(http.ResponseWriter, *http.Request, *adminauth.Session)) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		sess := s.session(r)
+		if sess == nil {
+			http.Redirect(w, r, "/login", http.StatusSeeOther)
+			return
+		}
+		if r.Method != http.MethodGet && r.Method != http.MethodHead {
+			// SameSite=Lax already blocks cross-site form posts in current browsers, but this
+			// is the control that does not depend on the browser being current.
+			if !s.csrfOK(r, sess) {
+				http.Error(w, "stale form — reload the page and try again", http.StatusForbidden)
+				return
+			}
+		}
+		h(w, r, sess)
+	}
+}
+
+func (s *Server) session(r *http.Request) *adminauth.Session {
+	c, err := r.Cookie(sessionCookie)
+	if err != nil {
+		return nil
+	}
+	sess, err := s.Sessions.Parse(c.Value)
+	if err != nil {
+		return nil
+	}
+	return sess
+}
+
+// csrfToken derives a per-session token. Derived rather than stored so it needs no server-side
+// state and cannot drift out of sync with the session it belongs to.
+func (s *Server) csrfToken(sess *adminauth.Session) string {
+	sum := sha256.Sum256([]byte("csrf|" + sess.Subject + "|" + sess.Expires.String()))
+	return base64.RawURLEncoding.EncodeToString(sum[:16])
+}
+
+func (s *Server) csrfOK(r *http.Request, sess *adminauth.Session) bool {
+	if err := r.ParseForm(); err != nil {
+		return false
+	}
+	return r.PostFormValue(csrfField) == s.csrfToken(sess)
+}
+
+func (s *Server) setSession(w http.ResponseWriter, subject, display string) {
+	http.SetCookie(w, &http.Cookie{
+		Name:     sessionCookie,
+		Value:    s.Sessions.Issue(subject, display),
+		Path:     "/",
+		HttpOnly: true, // the cookie is a bearer credential; script has no business reading it
+		Secure:   s.Secure,
+		SameSite: http.SameSiteLaxMode,
+	})
+}
+
+func (s *Server) logout(w http.ResponseWriter, r *http.Request) {
+	http.SetCookie(w, &http.Cookie{
+		Name: sessionCookie, Value: "", Path: "/", MaxAge: -1,
+		HttpOnly: true, Secure: s.Secure, SameSite: http.SameSiteLaxMode,
+	})
+	http.Redirect(w, r, "/login", http.StatusSeeOther)
+}
+
+// ---- local password ---------------------------------------------------------------------
+
+func (s *Server) loginSubmit(w http.ResponseWriter, r *http.Request) {
+	if err := r.ParseForm(); err != nil {
+		http.Error(w, "bad form", http.StatusBadRequest)
+		return
+	}
+	// The delay is applied before the answer, so a wrong guess costs time whether or not the
+	// username exists — the timing carries no information either way.
+	if d := s.Throttle.Delay(); d > 0 {
+		time.Sleep(d)
+	}
+	user := r.PostFormValue("username")
+	pass := r.PostFormValue("password")
+
+	cred := s.Store.LocalAdmin()
+	if cred == nil || !cred.Verify(user, pass) {
+		s.Throttle.Failed()
+		slog.Info("admin login failed", "user", user, "from", clientIP(r))
+		s.render(w, r, "login", map[string]any{
+			"Error": "Incorrect username or password.",
+			"OIDC":  s.oidcAvailable(),
+		})
+		return
+	}
+	s.Throttle.Succeeded()
+	slog.Info("admin login", "user", user, "method", "local", "from", clientIP(r))
+	s.setSession(w, "local:"+cred.Username, cred.Username)
+	http.Redirect(w, r, "/", http.StatusSeeOther)
+}
+
+// ---- OIDC -------------------------------------------------------------------------------
+
+func (s *Server) oidcAvailable() bool {
+	return s.OIDC != nil && s.OIDC.Config().Enabled() && s.BaseURL != ""
+}
+
+// oidcStart redirects to the IdP with state and PKCE.
+//
+// PKCE even though this is a confidential client: it costs one hash and closes code interception
+// independently of the secret, which is worth having when the redirect crosses a browser.
+func (s *Server) oidcStart(w http.ResponseWriter, r *http.Request) {
+	if !s.oidcAvailable() {
+		http.Error(w, "no identity provider is configured on this server", http.StatusNotImplemented)
+		return
+	}
+	d, err := s.OIDC.Discover(r.Context())
+	if err != nil {
+		http.Error(w, "identity provider unreachable: "+err.Error(), http.StatusBadGateway)
+		return
+	}
+	state, verifier := randomToken(), randomToken()
+	challenge := sha256.Sum256([]byte(verifier))
+
+	// state and the PKCE verifier ride in one short-lived cookie: the callback must prove it
+	// belongs to the browser that started the flow, or an attacker can feed us their own code.
+	http.SetCookie(w, &http.Cookie{
+		Name: stateCookie, Value: state + "." + verifier, Path: "/",
+		HttpOnly: true, Secure: s.Secure, SameSite: http.SameSiteLaxMode, MaxAge: 600,
+	})
+
+	q := url.Values{
+		"response_type":         {"code"},
+		"client_id":             {s.OIDC.Config().ClientID},
+		"redirect_uri":          {s.redirectURI()},
+		"scope":                 {"openid profile email"},
+		"state":                 {state},
+		"code_challenge":        {base64.RawURLEncoding.EncodeToString(challenge[:])},
+		"code_challenge_method": {"S256"},
+	}
+	http.Redirect(w, r, d.AuthorizationEndpoint+"?"+q.Encode(), http.StatusSeeOther)
+}
+
+func (s *Server) redirectURI() string {
+	return strings.TrimRight(s.BaseURL, "/") + "/admin/callback"
+}
+
+func (s *Server) oidcCallback(w http.ResponseWriter, r *http.Request) {
+	if !s.oidcAvailable() {
+		http.Error(w, "no identity provider configured", http.StatusNotImplemented)
+		return
+	}
+	c, err := r.Cookie(stateCookie)
+	if err != nil {
+		http.Error(w, "sign-in did not start here — try again from the login page", http.StatusBadRequest)
+		return
+	}
+	http.SetCookie(w, &http.Cookie{Name: stateCookie, Value: "", Path: "/", MaxAge: -1})
+
+	state, verifier, ok := strings.Cut(c.Value, ".")
+	if !ok || state == "" || r.URL.Query().Get("state") != state {
+		http.Error(w, "sign-in state did not match — start again", http.StatusBadRequest)
+		return
+	}
+	code := r.URL.Query().Get("code")
+	if code == "" {
+		http.Error(w, "no authorization code returned: "+r.URL.Query().Get("error"), http.StatusBadRequest)
+		return
+	}
+
+	idToken, err := s.exchange(r.Context(), code, verifier)
+	if err != nil {
+		slog.Info("admin oidc exchange failed", "err", err, "from", clientIP(r))
+		http.Error(w, "could not complete sign-in", http.StatusBadGateway)
+		return
+	}
+	claims, err := s.OIDC.Verify(r.Context(), idToken)
+	if err != nil {
+		slog.Info("admin oidc token rejected", "err", err, "from", clientIP(r))
+		http.Error(w, "the identity token was not accepted", http.StatusForbidden)
+		return
+	}
+	if !s.OIDC.IsAdmin(claims) {
+		// Named explicitly: "you signed in but you are not an admin" is a different problem from
+		// "your password is wrong", and the group is the thing to go and check.
+		slog.Info("admin access denied: not in group", "account", claims.AccountID(),
+			"want_group", s.OIDC.Config().AdminGroup, "have", claims.Groups)
+		http.Error(w, fmt.Sprintf(
+			"Signed in as %s, but that account is not in the %q group, so it cannot administer "+
+				"this server.", claims.Display(), s.OIDC.Config().AdminGroup), http.StatusForbidden)
+		return
+	}
+	slog.Info("admin login", "account", claims.AccountID(), "method", "oidc", "from", clientIP(r))
+	s.setSession(w, claims.AccountID(), claims.Display())
+	http.Redirect(w, r, "/", http.StatusSeeOther)
+}
+
+// exchange trades the authorization code for tokens at the IdP.
+func (s *Server) exchange(ctx context.Context, code, verifier string) (string, error) {
+	d, err := s.OIDC.Discover(ctx)
+	if err != nil {
+		return "", err
+	}
+	form := url.Values{
+		"grant_type":    {"authorization_code"},
+		"code":          {code},
+		"redirect_uri":  {s.redirectURI()},
+		"client_id":     {s.OIDC.Config().ClientID},
+		"code_verifier": {verifier},
+	}
+	if s.ClientSecret != "" {
+		form.Set("client_secret", s.ClientSecret)
+	}
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, d.TokenEndpoint,
+		strings.NewReader(form.Encode()))
+	if err != nil {
+		return "", err
+	}
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+
+	resp, err := (&http.Client{Timeout: 15 * time.Second}).Do(req)
+	if err != nil {
+		return "", err
+	}
+	defer resp.Body.Close()
+	body, _ := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
+	if resp.StatusCode != http.StatusOK {
+		return "", fmt.Errorf("token endpoint: %s: %s", resp.Status, strings.TrimSpace(string(body)))
+	}
+	var tok struct {
+		IDToken string `json:"id_token"`
+	}
+	if err := json.Unmarshal(body, &tok); err != nil {
+		return "", err
+	}
+	if tok.IDToken == "" {
+		return "", fmt.Errorf("token endpoint returned no id_token")
+	}
+	return tok.IDToken, nil
+}
+
+func randomToken() string {
+	b := make([]byte, 32)
+	_, _ = rand.Read(b)
+	return base64.RawURLEncoding.EncodeToString(b)
+}
+
+// clientIP is for logs only. X-Forwarded-For is deliberately ignored: nothing is meant to sit in
+// front of this listener, so a header claiming otherwise is a caller's assertion about itself.
+func clientIP(r *http.Request) string {
+	if i := strings.LastIndex(r.RemoteAddr, ":"); i > 0 {
+		return r.RemoteAddr[:i]
+	}
+	return r.RemoteAddr
+}

server/internal/adminui/pages.go

@@ -0,0 +1,168 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package adminui
+
+import (
+	"encoding/json"
+	"log/slog"
+	"net/http"
+	"net/url"
+	"sort"
+	"time"
+
+	"echo-lot.app/server/internal/adminauth"
+	"echo-lot.app/server/internal/runs"
+	"echo-lot.app/server/internal/store"
+)
+
+func (s *Server) loginForm(w http.ResponseWriter, r *http.Request) {
+	if s.session(r) != nil {
+		http.Redirect(w, r, "/", http.StatusSeeOther)
+		return
+	}
+	s.render(w, r, "login", map[string]any{
+		"OIDC":      s.oidcAvailable(),
+		"LocalSet":  s.Store.LocalAdmin() != nil,
+		"AdminUser": s.AdminUser,
+	})
+}
+
+func (s *Server) dashboard(w http.ResponseWriter, r *http.Request, sess *adminauth.Session) {
+	devices := s.Store.Devices()
+	linked := 0
+	for _, d := range devices {
+		if d.LinkedToAccount() {
+			linked++
+		}
+	}
+	var selftest any
+	if s.SelfTest != nil {
+		selftest = s.SelfTest()
+	}
+	s.render(w, r, "dashboard", map[string]any{
+		"Session":  sess,
+		"CSRF":     s.csrfToken(sess),
+		"Devices":  len(devices),
+		"Linked":   linked,
+		"Runs":     s.totalRuns(devices),
+		"SelfTest": selftest,
+		"Version":  s.Version,
+	})
+}
+
+func (s *Server) totalRuns(devices []store.Device) int {
+	if s.Runs == nil {
+		return 0
+	}
+	n := 0
+	for _, d := range devices {
+		n += len(s.Runs.List(d.ID))
+	}
+	return n
+}
+
+func (s *Server) devices(w http.ResponseWriter, r *http.Request, sess *adminauth.Session) {
+	devices := s.Store.Devices()
+	// Newest first: the device someone is looking for is almost always the one just enrolled.
+	sort.Slice(devices, func(i, j int) bool { return devices[i].Enrolled.After(devices[j].Enrolled) })
+
+	type row struct {
+		store.Device
+		Runs int
+	}
+	rows := make([]row, 0, len(devices))
+	for _, d := range devices {
+		n := 0
+		if s.Runs != nil {
+			n = len(s.Runs.List(d.ID))
+		}
+		rows = append(rows, row{Device: d, Runs: n})
+	}
+	s.render(w, r, "devices", map[string]any{
+		"Session": sess, "CSRF": s.csrfToken(sess), "Rows": rows,
+		"Link": r.URL.Query().Get("link"),
+	})
+}
+
+func (s *Server) revokeDevice(w http.ResponseWriter, r *http.Request, sess *adminauth.Session) {
+	id := r.PathValue("id")
+	if err := s.Store.DeleteDevice(id); err != nil {
+		http.Error(w, err.Error(), http.StatusBadRequest)
+		return
+	}
+	// Worth a log line: revoking a device is destructive, immediate, and someone will eventually
+	// want to know who did it and when.
+	slog.Info("device revoked", "device", id, "by", sess.Subject)
+	http.Redirect(w, r, "/devices", http.StatusSeeOther)
+}
+
+func (s *Server) mintToken(w http.ResponseWriter, r *http.Request, sess *adminauth.Session) {
+	tok, err := s.Store.NewEnrollToken(24*time.Hour, "admin-ui")
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	slog.Info("enrolment token minted", "by", sess.Subject)
+	// The whole link, not the bare token: it carries the URL and the pin as well, and assembling
+	// those by hand is where an operator gets a pin wrong by one character.
+	http.Redirect(w, r, "/devices?link="+url.QueryEscape(s.EnrollLink(tok)), http.StatusSeeOther)
+}
+
+// EnrollLink is supplied by the caller so this package does not need the control server's pin.
+var _ = 0
+
+func (s *Server) runsList(w http.ResponseWriter, r *http.Request, sess *adminauth.Session) {
+	type row struct {
+		runs.Meta
+		DeviceName string
+	}
+	var rows []row
+	for _, d := range s.Store.Devices() {
+		if s.Runs == nil {
+			break
+		}
+		name := d.Name
+		if name == "" {
+			name = d.ID
+		}
+		for _, m := range s.Runs.List(d.ID) {
+			rows = append(rows, row{Meta: m, DeviceName: name})
+		}
+	}
+	sort.Slice(rows, func(i, j int) bool { return rows[i].UploadedAt.After(rows[j].UploadedAt) })
+	if len(rows) > 200 {
+		rows = rows[:200] // a page, not the archive; the count is on the dashboard
+	}
+	s.render(w, r, "runs", map[string]any{"Session": sess, "CSRF": s.csrfToken(sess), "Rows": rows})
+}
+
+func (s *Server) runView(w http.ResponseWriter, r *http.Request, sess *adminauth.Session) {
+	body, err := s.Runs.Get(r.PathValue("device"), r.PathValue("id"))
+	if err != nil {
+		http.NotFound(w, r)
+		return
+	}
+	// Re-indented for reading, but otherwise exactly what was stored. An admin sees the document
+	// at the privacy level its uploader chose — there is nothing here that can un-redact it.
+	var pretty json.RawMessage = body
+	out, err := json.MarshalIndent(json.RawMessage(pretty), "", "  ")
+	if err != nil {
+		out = body
+	}
+	s.render(w, r, "run", map[string]any{
+		"Session": sess, "CSRF": s.csrfToken(sess),
+		"Device": r.PathValue("device"), "ID": r.PathValue("id"),
+		"JSON": string(out),
+	})
+}
+
+func (s *Server) runDelete(w http.ResponseWriter, r *http.Request, sess *adminauth.Session) {
+	device, id := r.PathValue("device"), r.PathValue("id")
+	if err := s.Runs.Delete(device, id); err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	slog.Info("run deleted", "device", device, "run", id, "by", sess.Subject)
+	http.Redirect(w, r, "/runs", http.StatusSeeOther)
+}

server/internal/adminui/render.go

@@ -0,0 +1,170 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package adminui
+
+import (
+	"bytes"
+	"html/template"
+	"log/slog"
+	"net/http"
+)
+
+// Templates are parsed once at start. html/template escapes by context, which is what makes it
+// safe to render device names and finding text that ultimately arrived over a network.
+var tpl = template.Must(template.New("base").Funcs(template.FuncMap{
+	"kb": func(n int64) int64 { return n / 1024 },
+}).Parse(baseHTML))
+
+func (s *Server) render(w http.ResponseWriter, r *http.Request, page string, data map[string]any) {
+	data["Page"] = page
+	var buf bytes.Buffer
+	if err := tpl.Execute(&buf, data); err != nil {
+		slog.Error("admin template", "page", page, "err", err)
+		http.Error(w, "template error", http.StatusInternalServerError)
+		return
+	}
+	w.Header().Set("Content-Type", "text/html; charset=utf-8")
+	// There is no script here and nothing loaded from anywhere else, so a strict policy costs
+	// nothing and closes injected-script attacks even if an escaping bug ever slips through.
+	w.Header().Set("Content-Security-Policy", "default-src 'none'; style-src 'unsafe-inline'; form-action 'self'")
+	w.Header().Set("Referrer-Policy", "no-referrer")
+	w.Header().Set("X-Content-Type-Options", "nosniff")
+	_, _ = buf.WriteTo(w)
+}
+
+const baseHTML = `<!doctype html>
+<html lang="en"><head><meta charset="utf-8">
+<meta name="viewport" content="width=device-width,initial-scale=1">
+<title>Echolot &mdash; {{.Page}}</title>
+<style>
+ :root{color-scheme:dark}
+ body{font:15px/1.5 system-ui,sans-serif;margin:0;background:#14161a;color:#e6e6e6}
+ header{display:flex;gap:1.2rem;align-items:baseline;padding:.8rem 1.2rem;background:#1c1f25;border-bottom:1px solid #2b2f36}
+ header h1{font-size:1.1rem;margin:0;font-weight:600}
+ header nav a{color:#9ecbff;text-decoration:none;margin-right:1rem}
+ header .who{margin-left:auto;color:#9aa3ad;font-size:.9rem}
+ main{padding:1.2rem;max-width:70rem}
+ table{border-collapse:collapse;width:100%;margin:.6rem 0}
+ th,td{text-align:left;padding:.45rem .6rem;border-bottom:1px solid #2b2f36;vertical-align:top}
+ th{color:#9aa3ad;font-weight:500;font-size:.85rem}
+ code,pre{font-family:ui-monospace,monospace;font-size:.85rem}
+ pre{background:#0f1114;padding:.8rem;border-radius:6px;overflow:auto;max-height:34rem}
+ .card{background:#1c1f25;border:1px solid #2b2f36;border-radius:8px;padding:1rem;margin:.8rem 0}
+ .grid{display:flex;gap:1rem;flex-wrap:wrap}
+ .stat{background:#1c1f25;border:1px solid #2b2f36;border-radius:8px;padding:.8rem 1.2rem;min-width:8rem}
+ .stat b{display:block;font-size:1.6rem;font-weight:600}
+ .stat span{color:#9aa3ad;font-size:.85rem}
+ button{font:inherit;background:#2d6cdf;color:#fff;border:0;border-radius:6px;padding:.4rem .8rem;cursor:pointer}
+ button.danger{background:#8b2f2f}
+ button.plain{background:#3a3f47}
+ input{font:inherit;background:#0f1114;color:#e6e6e6;border:1px solid #2b2f36;border-radius:6px;padding:.4rem .6rem}
+ .err{background:#3a1f1f;border:1px solid #7a3b3b;padding:.6rem .8rem;border-radius:6px}
+ .muted{color:#9aa3ad}
+ form.inline{display:inline}
+</style></head><body>
+{{if ne .Page "login"}}
+<header>
+  <h1>Echolot</h1>
+  <nav><a href="/">Overview</a><a href="/devices">Devices</a><a href="/runs">Runs</a></nav>
+  <span class="who">{{.Session.Display}}
+    <form method="post" action="/logout" class="inline"><button class="plain">Sign out</button></form>
+  </span>
+</header>
+{{end}}
+<main>
+
+{{if eq .Page "login"}}
+  <h2>Sign in</h2>
+  {{with .Error}}<p class="err">{{.}}</p>{{end}}
+  {{if .OIDC}}
+    <p><a href="/auth/start"><button>Sign in with your identity provider</button></a></p>
+    <p class="muted">or use the break-glass account:</p>
+  {{end}}
+  {{if .LocalSet}}
+    <form method="post" action="/login" class="card">
+      <p><label>Username<br><input name="username" value="{{.AdminUser}}" autocomplete="username"></label></p>
+      <p><label>Password<br><input name="password" type="password" autocomplete="current-password"></label></p>
+      <p><button>Sign in</button></p>
+    </form>
+  {{else}}
+    <p class="err">No break-glass admin is set. Run
+      <code>echolot-server --set-admin-password</code> on the host.</p>
+  {{end}}
+
+{{else if eq .Page "dashboard"}}
+  <div class="grid">
+    <div class="stat"><b>{{.Devices}}</b><span>devices</span></div>
+    <div class="stat"><b>{{.Linked}}</b><span>signed in</span></div>
+    <div class="stat"><b>{{.Runs}}</b><span>stored runs</span></div>
+  </div>
+  <div class="card">
+    <h3>Server</h3>
+    <p class="muted">version {{.Version}}</p>
+    {{with .SelfTest}}<pre>{{printf "%+v" .}}</pre>{{end}}
+  </div>
+
+{{else if eq .Page "devices"}}
+  <h2>Devices</h2>
+  {{with .Link}}
+  <div class="card">
+    <p><b>Enrolment link</b> &mdash; single use, valid 24 hours. Treat it like a password until spent.</p>
+    <p><code>{{.}}</code></p>
+    <p class="muted">On a device with adb:<br>
+      <code>adb shell am start -a android.intent.action.VIEW -d "{{.}}"</code></p>
+  </div>
+  {{end}}
+  <form method="post" action="/enroll-tokens">
+    <input type="hidden" name="csrf" value="{{.CSRF}}">
+    <button>Create enrolment link</button>
+  </form>
+  <table>
+    <tr><th>Device</th><th>Name</th><th>Account</th><th>Enrolled</th><th>Runs</th><th></th></tr>
+    {{range .Rows}}
+    <tr>
+      <td><code>{{.ID}}</code></td>
+      <td>{{if .Name}}{{.Name}}{{else}}<span class="muted">&mdash;</span>{{end}}</td>
+      <td>{{if .LinkedToAccount}}{{.AccountName}}{{else}}<span class="muted">not signed in</span>{{end}}</td>
+      <td>{{.Enrolled.Format "2006-01-02 15:04"}}</td>
+      <td>{{.Runs}}</td>
+      <td><form method="post" action="/devices/{{.ID}}/revoke" class="inline">
+        <input type="hidden" name="csrf" value="{{$.CSRF}}">
+        <button class="danger">Revoke</button></form></td>
+    </tr>
+    {{else}}
+    <tr><td colspan="6" class="muted">No devices enrolled.</td></tr>
+    {{end}}
+  </table>
+
+{{else if eq .Page "runs"}}
+  <h2>Uploaded runs</h2>
+  <p class="muted">Shown exactly as uploaded, at the privacy level the uploader chose. Nothing
+    here can un-redact a run.</p>
+  <table>
+    <tr><th>Uploaded</th><th>Device</th><th>Verdict</th><th>Findings</th><th>Size</th><th>Level</th><th></th></tr>
+    {{range .Rows}}
+    <tr>
+      <td>{{.UploadedAt.Format "2006-01-02 15:04"}}</td>
+      <td>{{.DeviceName}}</td>
+      <td>{{if .Verdict}}{{.Verdict}}{{else}}<span class="muted">&mdash;</span>{{end}}</td>
+      <td>{{.FindingCount}}</td>
+      <td>{{kb .SizeBytes}} kB</td>
+      <td>{{.Anonymization}}</td>
+      <td><a href="/runs/{{.DeviceID}}/{{.ID}}">open</a></td>
+    </tr>
+    {{else}}
+    <tr><td colspan="7" class="muted">Nothing uploaded yet.</td></tr>
+    {{end}}
+  </table>
+
+{{else if eq .Page "run"}}
+  <h2>Run {{.ID}}</h2>
+  <form method="post" action="/runs/{{.Device}}/{{.ID}}/delete" class="inline">
+    <input type="hidden" name="csrf" value="{{.CSRF}}">
+    <button class="danger">Delete this run</button>
+  </form>
+  <pre>{{.JSON}}</pre>
+{{end}}
+
+</main></body></html>
+`

server/internal/certreload/certreload.go

@@ -0,0 +1,124 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+// Package certreload serves a TLS certificate that can be replaced on disk without a restart.
+//
+// The hard part of TLS is never termination — the stdlib does that — it is renewal. A certificate
+// obtained from an ACME client expires every sixty days, and the usual arrangement is a renewal
+// hook that reloads or restarts the service. That hook is the part that quietly fails: it works
+// when it is written and then, months later, does not, and nobody notices until the certificate
+// has already expired.
+//
+// So the certificate is re-read when the file changes. There is no hook to forget, no reload to
+// coordinate, and a renewal that drops new files in place is picked up on the next handshake.
+//
+// Deliberately not used for the control plane. Clients pin that certificate's public key
+// (probe-protocol.md §1), so swapping it at runtime would silently break every enrolled device —
+// there the operator *should* have to think, and a restart is the least of what a key rotation
+// costs. Two listeners, two different right answers.
+package certreload
+
+import (
+	"crypto/tls"
+	"fmt"
+	"os"
+	"sync"
+	"time"
+)
+
+// Reloader holds a certificate and refreshes it when the files on disk change.
+type Reloader struct {
+	certPath, keyPath string
+
+	mu       sync.RWMutex
+	cert     *tls.Certificate
+	certMod  time.Time
+	keyMod   time.Time
+	checked  time.Time
+	interval time.Duration
+}
+
+// New loads the pair once so a bad path fails at startup rather than at the first handshake,
+// when the only symptom is a connection error at the far end.
+func New(certPath, keyPath string) (*Reloader, error) {
+	r := &Reloader{certPath: certPath, keyPath: keyPath, interval: 30 * time.Second}
+	if err := r.load(); err != nil {
+		return nil, err
+	}
+	return r, nil
+}
+
+// TLSConfig returns a config that asks this reloader for the certificate on every handshake.
+func (r *Reloader) TLSConfig() *tls.Config {
+	return &tls.Config{
+		MinVersion:     tls.VersionTLS12,
+		GetCertificate: r.getCertificate,
+	}
+}
+
+func (r *Reloader) getCertificate(*tls.ClientHelloInfo) (*tls.Certificate, error) {
+	r.maybeReload()
+	r.mu.RLock()
+	defer r.mu.RUnlock()
+	if r.cert == nil {
+		return nil, fmt.Errorf("no certificate loaded")
+	}
+	return r.cert, nil
+}
+
+// maybeReload stats the files at most once per interval.
+//
+// Rate-limited because this runs on every handshake: a busy listener would otherwise stat twice
+// per connection, and a certificate that is thirty seconds stale has never mattered to anyone.
+func (r *Reloader) maybeReload() {
+	r.mu.RLock()
+	fresh := time.Since(r.checked) < r.interval
+	r.mu.RUnlock()
+	if fresh {
+		return
+	}
+
+	r.mu.Lock()
+	r.checked = time.Now()
+	certMod, keyMod := modTime(r.certPath), modTime(r.keyPath)
+	unchanged := certMod.Equal(r.certMod) && keyMod.Equal(r.keyMod)
+	r.mu.Unlock()
+	if unchanged {
+		return
+	}
+	// A failed reload keeps the certificate already in memory. Renewal tools write the two files
+	// separately, so there is a window where the pair does not match; serving the previous
+	// certificate through that window is strictly better than serving none.
+	_ = r.load()
+}
+
+func (r *Reloader) load() error {
+	cert, err := tls.LoadX509KeyPair(r.certPath, r.keyPath)
+	if err != nil {
+		return fmt.Errorf("loading %s / %s: %w", r.certPath, r.keyPath, err)
+	}
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	r.cert = &cert
+	r.certMod, r.keyMod = modTime(r.certPath), modTime(r.keyPath)
+	return nil
+}
+
+// NotAfter is when the loaded certificate expires, for the admin UI to show and for a startup
+// warning. An expiry an operator can see is one they can act on before a browser tells them.
+func (r *Reloader) NotAfter() time.Time {
+	r.mu.RLock()
+	defer r.mu.RUnlock()
+	if r.cert == nil || r.cert.Leaf == nil {
+		return time.Time{}
+	}
+	return r.cert.Leaf.NotAfter
+}
+
+func modTime(path string) time.Time {
+	fi, err := os.Stat(path)
+	if err != nil {
+		return time.Time{}
+	}
+	return fi.ModTime()
+}

server/internal/certreload/certreload_test.go

@@ -0,0 +1,119 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package certreload
+
+import (
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/rand"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"encoding/pem"
+	"math/big"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+)
+
+func writePair(t *testing.T, dir, cn string) (string, string) {
+	t.Helper()
+	key, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+	if err != nil {
+		t.Fatal(err)
+	}
+	tmpl := x509.Certificate{
+		SerialNumber: big.NewInt(time.Now().UnixNano()),
+		Subject:      pkix.Name{CommonName: cn},
+		NotBefore:    time.Now().Add(-time.Hour),
+		NotAfter:     time.Now().Add(24 * time.Hour),
+	}
+	der, err := x509.CreateCertificate(rand.Reader, &tmpl, &tmpl, &key.PublicKey, key)
+	if err != nil {
+		t.Fatal(err)
+	}
+	certPath := filepath.Join(dir, "cert.pem")
+	keyPath := filepath.Join(dir, "key.pem")
+	cb := pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: der})
+	kb, _ := x509.MarshalECPrivateKey(key)
+	if err := os.WriteFile(certPath, cb, 0o600); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(keyPath, pem.EncodeToMemory(&pem.Block{Type: "EC PRIVATE KEY", Bytes: kb}), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	return certPath, keyPath
+}
+
+func TestBadPathsFailAtStartupNotAtHandshake(t *testing.T) {
+	if _, err := New("/nonexistent/cert.pem", "/nonexistent/key.pem"); err == nil {
+		t.Fatal("a missing certificate was accepted; the failure would surface as an " +
+			"unexplained connection error at the client instead")
+	}
+}
+
+// The whole point: a renewal that drops new files in place is picked up without a restart and
+// without a reload hook that can silently stop working.
+func TestANewCertificateOnDiskIsPickedUp(t *testing.T) {
+	dir := t.TempDir()
+	certPath, keyPath := writePair(t, dir, "first")
+	r, err := New(certPath, keyPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	r.interval = 0 // check on every handshake, rather than waiting out the rate limit
+
+	got, err := r.getCertificate(nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	first := got.Leaf
+
+	time.Sleep(10 * time.Millisecond) // ensure a distinct mtime
+	writePair(t, dir, "second")
+
+	got, err = r.getCertificate(nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got.Leaf != nil && first != nil && got.Leaf.SerialNumber.Cmp(first.SerialNumber) == 0 {
+		t.Fatal("the replaced certificate was not picked up")
+	}
+}
+
+// Renewal tools write the certificate and the key separately, so there is a window where the two
+// do not match. Serving the previous certificate through it beats serving none.
+func TestAHalfWrittenPairKeepsTheOldCertificate(t *testing.T) {
+	dir := t.TempDir()
+	certPath, keyPath := writePair(t, dir, "good")
+	r, err := New(certPath, keyPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	r.interval = 0
+
+	time.Sleep(10 * time.Millisecond)
+	if err := os.WriteFile(certPath, []byte("-----BEGIN CERTIFICATE-----\ntruncated\n"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	got, err := r.getCertificate(nil)
+	if err != nil {
+		t.Fatalf("a torn write took the listener down: %v", err)
+	}
+	if got == nil {
+		t.Fatal("no certificate served during a torn write")
+	}
+}
+
+func TestExpiryIsVisible(t *testing.T) {
+	dir := t.TempDir()
+	certPath, keyPath := writePair(t, dir, "x")
+	r, err := New(certPath, keyPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := r.NotAfter(); got.IsZero() || time.Until(got) > 48*time.Hour {
+		t.Fatalf("expiry not reported sensibly: %v", got)
+	}
+}

server/internal/config/config.go

@@ -10,6 +10,8 @@ package config
 import (
 	"flag"
 	"fmt"
+	"io"
+	"net"
 	"os"
 	"strconv"
 	"strings"
@@ -70,13 +72,60 @@ type Config struct {
 	// Identity provider. Empty issuer disables sign-in entirely; the server is a relying
 	// party and never stores passwords.
 	OIDCIssuer      string // ECHOLOT_OIDC_ISSUER / --oidc-issuer
-	OIDCClientID   string // ECHOLOT_OIDC_CLIENT_ID / --oidc-client-id
+	OIDCClientID    string // ECHOLOT_OIDC_CLIENT_ID / --oidc-client-id (confidential, admin UI)
+	OIDCAppClientID string // ECHOLOT_OIDC_APP_CLIENT_ID / --oidc-app-client-id (public, the phone app)
+	// Issuer for the app's client, when the IdP gives each application its own.
+	//
+	// Authentik derives the issuer from the application slug, so two applications mean two
+	// issuers — and a token's `iss` must match the one that minted it. Empty means both clients
+	// share ECHOLOT_OIDC_ISSUER, which is what IdPs with a single global issuer do.
+	OIDCAppIssuer  string // ECHOLOT_OIDC_APP_ISSUER / --oidc-app-issuer
 	OIDCAdminGroup string // ECHOLOT_OIDC_ADMIN_GROUP / --oidc-admin-group
 
+	// Break-glass admin username; the password lives hashed in the state store.
+	AdminUser string // ECHOLOT_ADMIN_USER / --admin-user
+
+	// Secret for the *confidential* admin client. Prefer ECHOLOT_OIDC_CLIENT_SECRET_FILE: a path
+	// keeps the secret out of the environment, where it is readable by anything that can see
+	// /proc/<pid>/environ and lands in every dump of the unit's configuration.
+	OIDCClientSecret string // ECHOLOT_OIDC_CLIENT_SECRET / _FILE
+
+	// Where the admin UI is reachable, used to build the OIDC redirect URI. Must match what is
+	// registered at the IdP exactly.
+	AdminBaseURL string // ECHOLOT_ADMIN_BASE_URL / --admin-base-url
+	// TLS for the admin listener. Without these it serves plaintext, which is only acceptable on
+	// loopback — see checkAdminExposure.
+	AdminTLSCert string // ECHOLOT_ADMIN_TLS_CERT / --admin-tls-cert
+	AdminTLSKey  string // ECHOLOT_ADMIN_TLS_KEY / --admin-tls-key
+	// Deliberate override for serving the admin UI in plaintext off loopback, so that decision
+	// is made rather than stumbled into.
+	AdminInsecure bool // ECHOLOT_ADMIN_INSECURE / --admin-insecure
+
+	// Port-80 listener that answers ACME HTTP-01 challenges and redirects everything else to
+	// the admin UI. Empty disables it. HTTP-01 always arrives on port 80 — the CA picks the
+	// port — so this never collides with the admin UI on 443.
+	ACMEHTTPListen string // ECHOLOT_ACME_HTTP_LISTEN / --acme-http-listen
+	// Directory an ACME client writes challenge tokens into. Defaults to <state-dir>/acme.
+	ACMEWebroot string // ECHOLOT_ACME_WEBROOT / --acme-webroot
+
 	// Mode
 	Docker bool // --docker (or autodetected; env ECHOLOT_DOCKER=1 forces)
 }
 
+// secretOr reads ECHOLOT_<key>, or the contents of the file named by ECHOLOT_<key>_FILE.
+//
+// The file form exists because a secret in the environment is readable by anything that can see
+// /proc/<pid>/environ and lands in every dump of the unit's configuration. A path costs nothing
+// and keeps the value in one file whose permissions an operator can reason about.
+func secretOr(key, def string) string {
+	if path := envOr(key+"_FILE", ""); path != "" {
+		if b, err := os.ReadFile(path); err == nil {
+			return strings.TrimSpace(string(b))
+		}
+	}
+	return envOr(key, def)
+}
+
 // envInt reads ECHOLOT_<key> as an integer with a fallback.
 func envInt(key string, def int) int {
 	if v := envOr(key, ""); v != "" {
@@ -122,8 +171,17 @@ func Load(args []string) (*Config, *Actions, error) {
 	fs.IntVar(&c.UploadMaxRuns, "upload-max-runs", envInt("UPLOAD_MAX_RUNS", 200), "keep at most this many runs per device; 0 disables")
 	fs.StringVar(&c.UploadMinAnon, "upload-min-anonymization", envOr("UPLOAD_MIN_ANONYMIZATION", "full"), "least anonymization accepted: full|balanced|strict")
 	fs.StringVar(&c.OIDCIssuer, "oidc-issuer", envOr("OIDC_ISSUER", ""), "OpenID Connect issuer URL; empty disables sign-in")
-	fs.StringVar(&c.OIDCClientID, "oidc-client-id", envOr("OIDC_CLIENT_ID", ""), "OpenID Connect client id for this server")
+	fs.StringVar(&c.OIDCClientID, "oidc-client-id", envOr("OIDC_CLIENT_ID", ""), "confidential OIDC client id for the admin UI")
+	fs.StringVar(&c.OIDCAppClientID, "oidc-app-client-id", envOr("OIDC_APP_CLIENT_ID", ""), "public OIDC client id used by the Android app (PKCE)")
+	fs.StringVar(&c.OIDCAppIssuer, "oidc-app-issuer", envOr("OIDC_APP_ISSUER", ""), "issuer for the app client when the IdP uses per-application issuers; empty = same as --oidc-issuer")
 	fs.StringVar(&c.OIDCAdminGroup, "oidc-admin-group", envOr("OIDC_ADMIN_GROUP", ""), "group claim required for admin access; empty means nobody is an admin via OIDC")
+	fs.StringVar(&c.OIDCClientSecret, "oidc-client-secret", secretOr("OIDC_CLIENT_SECRET", ""), "secret for the confidential admin client; prefer ECHOLOT_OIDC_CLIENT_SECRET_FILE")
+	fs.StringVar(&c.AdminBaseURL, "admin-base-url", envOr("ADMIN_BASE_URL", ""), "public URL of the admin UI, for the OIDC redirect (e.g. https://admin.example.net)")
+	fs.StringVar(&c.AdminTLSCert, "admin-tls-cert", envOr("ADMIN_TLS_CERT", ""), "TLS certificate for the admin listener")
+	fs.StringVar(&c.AdminTLSKey, "admin-tls-key", envOr("ADMIN_TLS_KEY", ""), "TLS key for the admin listener")
+	fs.BoolVar(&c.AdminInsecure, "admin-insecure", envOr("ADMIN_INSECURE", "") == "1", "allow the admin UI in plaintext off loopback (you are on your own)")
+	fs.StringVar(&c.ACMEHTTPListen, "acme-http-listen", envOr("ACME_HTTP_LISTEN", ""), "port-80 listener for ACME HTTP-01 challenges and http->https redirects")
+	fs.StringVar(&c.ACMEWebroot, "acme-webroot", envOr("ACME_WEBROOT", ""), "directory an ACME client writes challenges into (default <state-dir>/acme)")
 	fs.StringVar(&c.PublicControlURL, "public-url", envOr("PUBLIC_URL", ""), "public control-plane URL for enrollment links, e.g. https://probe.example.net:8443")
 	fs.StringVar(&c.MinAppVersion, "min-app-version", envOr("MIN_APP_VERSION", "0.2.0"), "oldest app version this server will serve (SemVer, inclusive)")
 	fs.StringVar(&c.MaxAppVersion, "max-app-version", envOr("MAX_APP_VERSION", "1.0.0"), "first app version this server will refuse (SemVer, exclusive); empty = unbounded")
@@ -131,6 +189,12 @@ func Load(args []string) (*Config, *Actions, error) {
 
 	fs.BoolVar(&a.InstallSystemd, "install-systemd", false, "install a systemd unit for this binary and exit")
 	fs.BoolVar(&a.UninstallSystemd, "uninstall-systemd", false, "remove the systemd unit and exit")
+	var daemon bool
+	fs.BoolVar(&a.Serve, "serve", false, "run the server (bind listeners and answer requests)")
+	fs.BoolVar(&daemon, "daemon", false, "alias for --serve")
+	fs.BoolVar(&a.SetAdminPassword, "set-admin-password", false,
+		"set the break-glass admin password (username as --admin-user, password read from stdin) and exit")
+	fs.StringVar(&c.AdminUser, "admin-user", envOr("ADMIN_USER", "admin"), "username for the break-glass admin")
 	fs.BoolVar(&a.SelfUpdate, "self-update", false, "check for a newer release, replace this binary, and exit")
 	fs.BoolVar(&a.Version, "version", false, "print version and exit")
 
@@ -140,12 +204,78 @@ func Load(args []string) (*Config, *Actions, error) {
 	if !c.Docker {
 		c.Docker = inContainer()
 	}
+	a.Serve = a.Serve || daemon
+	// No verb at all means the caller has not said what they want. Usage is the answer, and it
+	// is a usage error rather than success — otherwise a service manager sees a clean exit and
+	// concludes the server ran and finished.
+	if !a.Serve && !a.InstallSystemd && !a.UninstallSystemd && !a.SelfUpdate &&
+		!a.SetAdminPassword && !a.Version {
+		a.Help = true
+	}
+	if a.Serve {
+		if err := c.checkAdminExposure(); err != nil {
+			return nil, nil, err
+		}
+	}
 	if c.Docker && (a.InstallSystemd || a.UninstallSystemd || a.SelfUpdate) {
 		return nil, nil, fmt.Errorf("systemd/self-update actions are native-mode only (container detected; override with ECHOLOT_DOCKER=0 if this is wrong)")
 	}
 	return c, a, nil
 }
 
+// Usage prints the verbs first and the tuning flags second, because the question someone has
+// when they run this by name is "what does it do", not "what can I set".
+func Usage(w io.Writer) {
+	fmt.Fprint(w, `echolot-server — the Echolot probe server
+
+USAGE
+  echolot-server --serve                 run the server
+  echolot-server --version               print the version
+  echolot-server --install-systemd       install and enable a systemd unit
+  echolot-server --uninstall-systemd     remove it
+  echolot-server --self-update           replace this binary with the latest release
+  echolot-server --set-admin-password    set the break-glass admin password (stdin)
+  echolot-server --help                  full flag list
+
+Every flag can also be set as an environment variable: --control-listen becomes
+ECHOLOT_CONTROL_LISTEN. In a container, configuration comes from the environment.
+
+Running with no verb prints this and exits non-zero: starting to serve the internet
+should be something you asked for.
+`)
+}
+
+// checkAdminExposure refuses to serve an unencrypted admin UI on a non-loopback address.
+//
+// The admin session cookie is a bearer credential for everything this server can do, and the OIDC
+// authorization code arrives in a URL. In plaintext, both are readable by anyone on the path — and
+// on a globally routable address "the path" means the internet. This is a hard stop rather than a
+// warning because a warning in a log is not read by the person who most needs it, and because the
+// two safe answers are cheap: bind to loopback and tunnel, or supply a certificate.
+func (c *Config) checkAdminExposure() error {
+	if c.AdminTLSCert != "" || c.AdminInsecure {
+		return nil
+	}
+	for _, addr := range Addrs(c.AdminListen) {
+		host, _, err := net.SplitHostPort(addr)
+		if err != nil {
+			continue
+		}
+		ip := net.ParseIP(strings.Trim(host, "[]"))
+		if host == "" || ip == nil || ip.IsLoopback() {
+			continue // loopback, or a name we cannot judge; RFC 8252 blesses loopback plaintext
+		}
+		return fmt.Errorf(
+			"refusing to serve the admin UI in plaintext on %s: the session cookie and the OIDC "+
+				"authorization code would cross the network in the clear.\n"+
+				"  Fix it one of three ways:\n"+
+				"    - bind to 127.0.0.1 and reach it over an SSH tunnel (no certificate needed)\n"+
+				"    - set ECHOLOT_ADMIN_TLS_CERT and ECHOLOT_ADMIN_TLS_KEY\n"+
+				"    - set ECHOLOT_ADMIN_INSECURE=1 if you genuinely mean it", addr)
+	}
+	return nil
+}
+
 // Addrs splits a comma-separated listen spec into individual addresses.
 // Explicit per-address binds matter on multi-IP hosts: a wildcard bind
 // (":8443") would also claim addresses reserved for other purposes (e.g. an
@@ -160,11 +290,19 @@ func Addrs(spec string) []string {
 	return out
 }
 
-// Actions are one-shot verbs that exit instead of serving.
+// Actions are the verbs. Serving is one of them, and it is explicit: running the binary with no
+// arguments prints usage rather than binding a dozen ports and starting to answer the internet.
+// Someone typing the name of an unfamiliar program on a terminal should be told what it does, not
+// have it start doing it.
 type Actions struct {
+	Serve bool
+	// Help is set when there is nothing to do: no verb was given.
+	Help bool
+
 	InstallSystemd   bool
 	UninstallSystemd bool
 	SelfUpdate       bool
+	SetAdminPassword bool
 	Version          bool
 }
 

server/internal/control/control.go

@@ -59,8 +59,12 @@ type Server struct {
 	// Granted server->client sends (spec §5). Both consume an asymmetric grant.
 	DownTrain func(sess *session.Session, g *session.Grant, count, sizeBytes, intervalUs int) (int, error)
 	BigSend   func(sess *session.Session, g *session.Grant, sizes []int, df bool) ([]dataplane.BigSendResult, error)
-	// OIDC verifies ID tokens when the operator has configured an issuer (may be nil).
+	// OIDC verifies ID tokens presented by the *app* (may be nil).
 	OIDC *oidc.Verifier
+	// AdminOIDC verifies tokens from the admin UI's own client. Separate because an IdP may
+	// give each application its own issuer — Authentik derives it from the application slug —
+	// and a verifier pins exactly one issuer and the clients belonging to it.
+	AdminOIDC *oidc.Verifier
 	// Runs stores uploaded measurement documents (may be nil: uploads unsupported).
 	Runs *runs.Store
 	// FragSend emits one datagram as hand-built IP fragments in a chosen order (may be nil:
@@ -830,7 +834,8 @@ func (s *Server) authInfo(ctx context.Context) map[string]any {
 	out := map[string]any{
 		"enabled": true,
 		"issuer":  cfg.Issuer,
-		"client_id": cfg.ClientID,
+		// The app's client, not the server's: this is what a phone should authorize as.
+		"client_id": cfg.AppClientID,
 		// The app is a public client on a phone: no secret can be kept, so PKCE is what
 		// protects the code exchange (RFC 7636), and the redirect comes back through the
 		// scheme the app already registers for enrollment links.

server/internal/oidc/oidc.go

@@ -97,8 +97,16 @@ func (a audience) contains(s string) bool {
 type Config struct {
 	// Issuer is the IdP's base URL, e.g. https://auth.example.net/application/o/echolot/
 	Issuer string
-	// ClientID is this server's registered client. Tokens must be addressed to it.
+	// ClientID is this server's own registered client — confidential, used for the admin UI's
+	// browser login, where a secret can genuinely be kept in the host's config.
 	ClientID string
+	// AppClientID is the mobile app's registered client. It is a separate, *public* client
+	// because an APK cannot keep a secret, so it uses PKCE instead.
+	//
+	// Both are accepted as audiences, and they must be listed rather than merged: a token is
+	// addressed to a specific client, and accepting "any client of this issuer" would let every
+	// other application registered with the same IdP authenticate here.
+	AppClientID string
 	// AdminGroup, when set, is the group claim a person must hold to reach the admin UI.
 	// Empty means no one is an admin via OIDC, which is the safe default: an operator who has
 	// not said who may administer the server has not said "everyone".
@@ -107,7 +115,27 @@ type Config struct {
 	Skew time.Duration
 }
 
-func (c Config) Enabled() bool { return c.Issuer != "" && c.ClientID != "" }
+func (c Config) Enabled() bool { return c.Issuer != "" && (c.ClientID != "" || c.AppClientID != "") }
+
+// acceptedAudiences is every client id this server answers for.
+func (v *Verifier) acceptedAudiences() []string {
+	out := make([]string, 0, 2)
+	for _, id := range []string{v.cfg.ClientID, v.cfg.AppClientID} {
+		if id != "" {
+			out = append(out, id)
+		}
+	}
+	return out
+}
+
+func (v *Verifier) audienceAccepted(aud audience) bool {
+	for _, id := range v.acceptedAudiences() {
+		if aud.contains(id) {
+			return true
+		}
+	}
+	return false
+}
 
 // Discovery is the subset of the provider metadata document that is used.
 type Discovery struct {
@@ -362,8 +390,9 @@ func (v *Verifier) checkClaims(c Claims) error {
 	}
 	// A token addressed to a different client is a valid token that was not meant for us —
 	// accepting it lets any other client of the same IdP authenticate here.
-	if !c.Audience.contains(v.cfg.ClientID) {
+	if !v.audienceAccepted(c.Audience) {
-		return fmt.Errorf("%w: addressed to %v, not to %q", ErrClaims, []string(c.Audience), v.cfg.ClientID)
+		return fmt.Errorf("%w: addressed to %v, not to %v", ErrClaims,
+			[]string(c.Audience), v.acceptedAudiences())
 	}
 	if c.Subject == "" {
 		return fmt.Errorf("%w: no subject", ErrClaims)

server/internal/oidc/oidc_test.go

@@ -115,7 +115,9 @@ func (i *testIdP) claims(extra map[string]any) map[string]any {
 }
 
 func verifier(i *testIdP, adminGroup string) *Verifier {
-	return New(Config{Issuer: i.URL, ClientID: "echolot", AdminGroup: adminGroup}, i.Client())
+	return New(Config{
+		Issuer: i.URL, ClientID: "echolot", AppClientID: "echolot-app", AdminGroup: adminGroup,
+	}, i.Client())
 }
 
 func TestAcceptsAGenuineToken(t *testing.T) {
@@ -286,3 +288,38 @@ func TestDisabledWithoutConfiguration(t *testing.T) {
 		t.Fatalf("want ErrDisabled, got %v", err)
 	}
 }
+
+// Two clients, because the phone and the admin UI have different properties: an APK cannot keep a
+// secret (public + PKCE) while the server can (confidential). Both must be accepted — but only
+// those two. "Any client of this issuer" would let every other application registered with the
+// same IdP authenticate here, which is the whole reason the audience check exists.
+func TestBothRegisteredClientsAreAccepted(t *testing.T) {
+	idp := newIdP(t)
+	v := verifier(idp, "")
+
+	for _, aud := range []any{"echolot", "echolot-app", []string{"echolot-app", "other"}} {
+		tok := idp.sign(t, "RS256", "rsa-1", idp.claims(map[string]any{"aud": aud}))
+		if _, err := v.Verify(context.Background(), tok); err != nil {
+			t.Errorf("aud %v was refused: %v", aud, err)
+		}
+	}
+	// A third application at the same issuer is still not us.
+	tok := idp.sign(t, "RS256", "rsa-1", idp.claims(map[string]any{"aud": "someone-elses-app"}))
+	if _, err := v.Verify(context.Background(), tok); !errors.Is(err, ErrClaims) {
+		t.Fatalf("a third client's token was accepted: %v", err)
+	}
+}
+
+// Either client id alone is enough to make sign-in usable: an operator may register only the app
+// (no admin UI login) or only the server.
+func TestEitherClientIDAloneEnablesSignIn(t *testing.T) {
+	if !(Config{Issuer: "https://i", ClientID: "a"}).Enabled() {
+		t.Error("a server-only configuration was reported disabled")
+	}
+	if !(Config{Issuer: "https://i", AppClientID: "b"}).Enabled() {
+		t.Error("an app-only configuration was reported disabled")
+	}
+	if (Config{Issuer: "https://i"}).Enabled() {
+		t.Error("an issuer with no client at all was reported enabled")
+	}
+}

server/internal/selfupdate/selfupdate.go

@@ -9,6 +9,7 @@ package selfupdate
 
 import (
 	"crypto/sha256"
+	"echo-lot.app/server/internal/system"
 	"encoding/hex"
 	"encoding/json"
 	"fmt"
@@ -132,6 +133,15 @@ func Run(api, currentVersion string) error {
 		os.Remove(tmp)
 		return fmt.Errorf("atomic replace failed (filesystem boundaries?): %w", err)
 	}
+	// Serving became an explicit verb, and a unit written before that change starts this binary
+	// with no arguments - which now prints usage and exits non-zero. The unit is not part of what
+	// an update replaces, so it is repaired here rather than left to fail at the next restart,
+	// which might be a reboot months from now.
+	if repaired, err := system.RepairExecStart(); err != nil {
+		fmt.Println("WARNING: could not update the systemd unit for --serve:", err)
+	} else if repaired {
+		fmt.Println("updated the systemd unit to pass --serve (serving is now an explicit verb)")
+	}
 	fmt.Printf("updated %s -> %s (%s); restart to run it\n", currentVersion, rel.TagName, self)
 	return nil
 }

server/internal/store/store.go

@@ -16,6 +16,8 @@ import (
 	"os"
 	"path/filepath"
 	"sync"
+
+	"echo-lot.app/server/internal/adminauth"
 	"time"
 )
 
@@ -59,6 +61,12 @@ type Store struct {
 type fileData struct {
 	Tokens  []EnrollToken `json:"tokens"`
 	Devices []Device      `json:"devices"`
+	// The break-glass admin. Absent until an operator sets one.
+	LocalAdmin *adminauth.Credential `json:"local_admin,omitempty"`
+	// Signing secret for admin session cookies. Persisted so sessions survive a restart;
+	// deleting it from the state file invalidates every session at once, which is how an
+	// operator revokes them.
+	SessionSecret string `json:"session_secret,omitempty"`
 }
 
 func Open(stateDir string) (*Store, error) {
@@ -177,6 +185,50 @@ func (s *Store) DeleteDevice(id string) error {
 	return errors.New("no such device")
 }
 
+// SetLocalAdmin stores (or replaces) the break-glass admin password.
+func (s *Store) SetLocalAdmin(c adminauth.Credential) error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	s.data.LocalAdmin = &c
+	return s.save()
+}
+
+// LocalAdmin returns the configured break-glass admin, or nil.
+func (s *Store) LocalAdmin() *adminauth.Credential {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if s.data.LocalAdmin == nil {
+		return nil
+	}
+	c := *s.data.LocalAdmin
+	return &c
+}
+
+// ClearLocalAdmin removes the break-glass admin.
+func (s *Store) ClearLocalAdmin() error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	s.data.LocalAdmin = nil
+	return s.save()
+}
+
+// SessionSecret returns the admin session signing secret, creating one on first use.
+func (s *Store) SessionSecret() ([]byte, error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	if s.data.SessionSecret != "" {
+		if b, err := hex.DecodeString(s.data.SessionSecret); err == nil && len(b) >= 32 {
+			return b, nil
+		}
+	}
+	b, err := adminauth.NewSecret()
+	if err != nil {
+		return nil, err
+	}
+	s.data.SessionSecret = hex.EncodeToString(b)
+	return b, s.save()
+}
+
 func (s *Store) DeviceByCredential(cred string) *Device {
 	s.mu.Lock()
 	defer s.mu.Unlock()

server/internal/system/echo_linux.go

@@ -0,0 +1,34 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+//go:build linux
+
+package system
+
+import (
+	"os"
+	"syscall"
+	"unsafe"
+)
+
+// DisableEcho turns off terminal echo while a password is typed, returning a function that puts
+// the terminal back. Both are best-effort: when stdin is a pipe (the automation case) there is
+// no terminal to change and nothing to restore.
+func DisableEcho(f *os.File) (func(), error) {
+	fd := f.Fd()
+	var t syscall.Termios
+	if _, _, errno := syscall.Syscall6(syscall.SYS_IOCTL, fd,
+		syscall.TCGETS, uintptr(unsafe.Pointer(&t)), 0, 0, 0); errno != 0 {
+		return nil, errno // not a terminal; nothing to do
+	}
+	original := t
+	t.Lflag &^= syscall.ECHO
+	if _, _, errno := syscall.Syscall6(syscall.SYS_IOCTL, fd,
+		syscall.TCSETS, uintptr(unsafe.Pointer(&t)), 0, 0, 0); errno != 0 {
+		return nil, errno
+	}
+	return func() {
+		_, _, _ = syscall.Syscall6(syscall.SYS_IOCTL, fd,
+			syscall.TCSETS, uintptr(unsafe.Pointer(&original)), 0, 0, 0)
+	}, nil
+}

server/internal/system/echo_other.go

@@ -0,0 +1,12 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+//go:build !linux
+
+package system
+
+import "os"
+
+// DisableEcho is a no-op off Linux: the password is still read, just echoed. Better than
+// refusing to run — an operator on a Mac still needs to set the break-glass password.
+func DisableEcho(*os.File) (func(), error) { return nil, nil }

server/internal/system/systemd.go

@@ -12,6 +12,7 @@ import (
 	"os/exec"
 	"path/filepath"
 	"runtime"
+	"strings"
 )
 
 const (
@@ -29,7 +30,7 @@ Wants=network-online.target
 
 [Service]
 Type=simple
-ExecStart=%s
+ExecStart=%s --serve
 Restart=on-failure
 RestartSec=5
 StateDirectory=echolot-server
@@ -144,3 +145,41 @@ func UninstallSystemd() error {
 	fmt.Println("removed echolot-server units (state dir and env file left in place)")
 	return nil
 }
+
+// RepairExecStart brings an already-installed unit up to date with the current invocation.
+//
+// Serving became an explicit verb (--serve), which means every unit written before that change
+// would start the binary with no arguments — and the binary now answers that with usage and a
+// non-zero exit. A self-update replaces the binary but never the unit, so without this a routine
+// update would leave a service that cannot start, discovered whenever the host next reboots.
+//
+// Only a unit this program wrote is touched, identified by its description line. Editing an
+// operator's hand-written unit would be overreach; leaving ours broken would be negligence.
+func RepairExecStart() (repaired bool, err error) {
+	b, err := os.ReadFile(unitPath)
+	if err != nil {
+		return false, nil // no unit installed: nothing to repair, and not an error
+	}
+	text := string(b)
+	if !strings.Contains(text, "Echolot probe server") {
+		return false, nil // somebody else's unit
+	}
+	lines := strings.Split(text, "\n")
+	changed := false
+	for i, ln := range lines {
+		t := strings.TrimSpace(ln)
+		// Only the serving unit's ExecStart; the timer's own line already carries its verb.
+		if strings.HasPrefix(t, "ExecStart=") && !strings.Contains(t, "--") {
+			lines[i] = ln + " --serve"
+			changed = true
+		}
+	}
+	if !changed {
+		return false, nil
+	}
+	if err := os.WriteFile(unitPath, []byte(strings.Join(lines, "\n")), 0o644); err != nil {
+		return false, fmt.Errorf("updating %s: %w", unitPath, err)
+	}
+	_ = exec.Command("systemctl", "daemon-reload").Run()
+	return true, nil
+}