Phase 2: SQLite persistence, admin setup-link, login/sessions

Implements the secure single-admin panel entry (spec 7.6).

- internal/store: modernc.org/sqlite (pure Go, static build), WAL +
  foreign keys, embedded PRAGMA user_version migrations; schema 0001
  covers admin/settings/domains/applications/send_log/rate_limits (spec 9).
- Setup secret-link (spec 7.6.1): 128-bit crypto/rand token, printed to
  log + /data/setup-token (0600), 10-min TTL with regeneration, per-IP
  rate limit, subtle.ConstantTimeCompare, failures don't invalidate,
  one-time admin form, permanent invalidation once admin exists (/setup 404).
- bcrypt admin password; server-side username/password validation.
- Login + in-memory sessions, crypto-random token, cookie
  HttpOnly/Secure/SameSite (Secure toggleable for dev HTTP), login
  rate limit, auth middleware.
- html/template base layout + setup/login/dashboard, vendored htmx 2.0.4.
- build/entrypoint.sh: fix bind-mounted /data ownership as root before
  supervisord drops to the unprivileged panel user (found via container test).

Verified on selfpost.mixfed.ru: go vet/build/test/gofmt clean; e2e curl
of setup+login flows; docker build + run with -v ./data:/data creates the
DB and 0600 token owned by panel.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

internal/web/setup.go

@@ -0,0 +1,136 @@
+package web
+
+import (
+	"crypto/subtle"
+	"fmt"
+	"os"
+	"sync"
+	"time"
+
+	"codeberg.org/mix/selfpost/internal/store"
+)
+
+// setupTokenTTL is the lifetime of a setup token (spec 7.6.1). After it
+// elapses the token is regenerated and re-announced on the next /setup hit.
+const setupTokenTTL = 10 * time.Minute
+
+// setupManager owns the one-time administrator setup token. The token itself is
+// ephemeral (regenerated on restart or expiry) and lives only in memory; the
+// persistent "setup complete" fact is the presence of the admin row in the
+// store, so once that exists the token is gone for good (spec 7.6.1).
+type setupManager struct {
+	store     *store.Store
+	hostname  string
+	tokenPath string
+
+	mu        sync.Mutex
+	token     string
+	expiresAt time.Time
+}
+
+func newSetupManager(st *store.Store, hostname, tokenPath string) *setupManager {
+	return &setupManager{store: st, hostname: hostname, tokenPath: tokenPath}
+}
+
+// bootstrap runs once at startup. If setup is already complete it clears any
+// stale token file; otherwise it mints and announces the first token.
+func (m *setupManager) bootstrap() error {
+	done, err := m.store.AdminExists()
+	if err != nil {
+		return err
+	}
+	if done {
+		m.clearTokenFile()
+		return nil
+	}
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	m.regenerateLocked()
+	return nil
+}
+
+// activeToken returns the current valid setup token, regenerating and
+// re-announcing it if none exists or it has expired. It returns ("", false)
+// once setup is complete — callers must treat that as "route gone" (404).
+func (m *setupManager) activeToken() (string, bool) {
+	done, err := m.store.AdminExists()
+	if err != nil {
+		logf("panel: setup: admin check failed: %v", err)
+		return "", false
+	}
+	if done {
+		return "", false
+	}
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	if m.token == "" || time.Now().After(m.expiresAt) {
+		m.regenerateLocked()
+	}
+	return m.token, true
+}
+
+// validate reports whether provided matches the active token, using a
+// constant-time comparison to avoid leaking a correct prefix via timing
+// (spec 7.6.1). A mismatch does NOT regenerate or invalidate the token: failed
+// attempts must not let an attacker DoS a legitimate setup (spec 7.6.1).
+func (m *setupManager) validate(provided string) bool {
+	token, ok := m.activeToken()
+	if !ok {
+		return false
+	}
+	return subtle.ConstantTimeCompare([]byte(provided), []byte(token)) == 1
+}
+
+// complete marks setup as finished: the admin row now exists, so drop the
+// in-memory token and remove the on-disk copy.
+func (m *setupManager) complete() {
+	m.mu.Lock()
+	m.token = ""
+	m.expiresAt = time.Time{}
+	m.mu.Unlock()
+	m.clearTokenFile()
+}
+
+// regenerateLocked mints a fresh token, announces it and mirrors it to disk.
+// Caller holds m.mu.
+func (m *setupManager) regenerateLocked() {
+	m.token = randomToken(16) // 128 bits of entropy (spec 7.6.1)
+	m.expiresAt = time.Now().Add(setupTokenTTL)
+	m.announce(m.token)
+}
+
+// announce prints the setup link to the container log and writes it to the
+// token file so it can be read either way (spec 7.6.1).
+func (m *setupManager) announce(token string) {
+	url := m.setupURL(token)
+	logf("panel: ==================================================================")
+	logf("panel: SelfPost first-run setup — open this one-time link within %s:", setupTokenTTL)
+	logf("panel:   %s", url)
+	logf("panel: (also written to %s)", m.tokenPath)
+	logf("panel: ==================================================================")
+
+	if m.tokenPath == "" {
+		return
+	}
+	// 0600: the token is a bearer secret for creating the admin.
+	if err := os.WriteFile(m.tokenPath, []byte(url+"\n"), 0o600); err != nil {
+		logf("panel: setup: could not write token file %s: %v", m.tokenPath, err)
+	}
+}
+
+func (m *setupManager) setupURL(token string) string {
+	host := m.hostname
+	if host == "" {
+		host = "localhost"
+	}
+	return fmt.Sprintf("https://%s/setup/%s", host, token)
+}
+
+func (m *setupManager) clearTokenFile() {
+	if m.tokenPath == "" {
+		return
+	}
+	if err := os.Remove(m.tokenPath); err != nil && !os.IsNotExist(err) {
+		logf("panel: setup: could not remove token file %s: %v", m.tokenPath, err)
+	}
+}