panel-redesign: security review of 2.0 - sessions belong to a user by id

Stage 3, step 2. Reviewed by Fable (read-only), fixed by Sonnet with a
failing test before each fix, checked by Opus. No Critical or High
finding: route authorization, tenant isolation by id, the /server/
subtree guard, output encoding and the origin check were found sound.

Fixed
  - M1: a session was keyed by user name and had no link to the user. A
    deleted or renamed user's cookie stayed alive (renewed on every hit,
    before the user was looked up) and became a session of whoever was
    later created under that name, with that account's role. The
    baseline now has sessions.user_id REFERENCES users(id) ON DELETE
    CASCADE; the principal is resolved by id and a session is renewed
    only after its user was found. RenameSession is gone.
  - M2: any user's password change deleted every other user's sessions.
    It ends that user's other sessions only.
  - L1: a password set on the user form ends that user's sessions (an
    administrator editing their own account keeps the current one).
  - L2: store, saslpasswd2 and Postfix reload errors were shown verbatim
    on the application form, the inbound upstream / recipients forms and
    the limit recalculation - pages a domain administrator reaches.
    Validation errors (app.ValidationError, inbound.ValidationError,
    store.ErrNotAutoRateLimit) keep their text; anything else is logged
    and shown as "Could not save ... Check the logs and try again."
  - L3: store.ListDMARCReports treated an empty domain list as "all". It
    takes a scope now (AllDomains or a list; an empty list is no rows),
    and the DMARC hub is open to the domain role as the plan says: the
    reports of the assigned domains, without the instance-wide ingest
    box. The menu entry was already shown to them and led to a 404.
  - I1: /static/ answered with a listing of the embedded assets. A path
    that is not a known asset is a 404.

Consequences
  - The global DMARC hub lists reports of domains that were deleted
    since, too.
  - dev/migrate1x (not in the tree) no longer carries sessions over:
    everyone signs in again after the transfer.
  - docs/schema-migrations.md: the sessions row.

Recorded, not changed - for the owner:
  - L4: the report-address select names the followed user and their
    address to every administrator of the domain, by default the global
    administrator's login name. The plan asks for it.
  - L5: a delegated inbound upstream may be any host and port, loopback
    and private ranges included - within the trusted-operator model; to
    be listed among the accepted risks in security.md.
  - L6: Account's profile is saved without the password; becomes a
    requirement once password-reset mails to users.email.
  - Still echoing an error's text: backup and domain import (global
    only), the domain form's validation messages.

Not checked by the review: anything needing the container (e2e, real
Postfix / DNS), CSP behaviour in a live browser.

  go test -count=1 ./internal/web/... ./internal/store/... ./internal/app/...
    ./internal/inbound/... ./internal/dmarc/... ./cmd/panel
      ok  (all eleven packages; dev/migrate1x also ok)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/web/auth/session.go

@@ -41,14 +41,14 @@ func hashToken(token string) string {
 	return hex.EncodeToString(sum[:])
 }
 
-// Create issues a new session for username and returns its token. It fails
+// Create issues a new session for the user and returns its token. It fails
 // closed: if the row cannot be written the caller gets an error and must not
 // hand out a cookie, because a token that is not in the database looks like a
 // signed-in browser while every request it makes bounces back to /login.
-func (s *sessionStore) Create(username string) (string, error) {
+func (s *sessionStore) Create(userID int64) (string, error) {
 	token := randomToken(32)
 	now := time.Now()
-	if err := s.store.CreateSession(hashToken(token), username, now.Add(s.idle)); err != nil {
+	if err := s.store.CreateSession(hashToken(token), userID, now.Add(s.idle)); err != nil {
 		return "", err
 	}
 	// Pruning is housekeeping: the new session is already valid, so a failure
@@ -59,28 +59,28 @@ func (s *sessionStore) Create(username string) (string, error) {
 	return token, nil
 }
 
-// Lookup returns the session username for a token if it exists and is
-// unexpired.
-func (s *sessionStore) Lookup(token string) (string, bool) {
+// Lookup returns the id of the user a token's session belongs to, if the
+// session exists and is unexpired.
+func (s *sessionStore) Lookup(token string) (int64, bool) {
 	if token == "" {
-		return "", false
+		return 0, false
 	}
 	hash := hashToken(token)
 	row, found, err := s.store.LookupSession(hash)
 	if err != nil {
 		logf("panel: session: lookup failed: %v", err)
-		return "", false
+		return 0, false
 	}
 	if !found {
-		return "", false
+		return 0, false
 	}
 	if time.Now().After(row.ExpiresAt) {
 		if err := s.store.DeleteSession(hash); err != nil {
 			logf("panel: session: delete expired failed: %v", err)
 		}
-		return "", false
+		return 0, false
 	}
-	return row.Username, true
+	return row.UserID, true
 }
 
 // Touch extends a session's sliding expiry if it has been at least
@@ -107,17 +107,17 @@ func (s *sessionStore) Touch(token string) bool {
 	return true
 }
 
-// Rename updates the username carried by a session, keeping its expiry.
-func (s *sessionStore) Rename(token, username string) {
-	if err := s.store.RenameSession(hashToken(token), username); err != nil {
-		logf("panel: session: rename failed: %v", err)
+// DestroyOthers invalidates every session of the user except keep.
+func (s *sessionStore) DestroyOthers(userID int64, keep string) {
+	if err := s.store.DeleteOtherSessions(userID, hashToken(keep)); err != nil {
+		logf("panel: session: destroy others failed: %v", err)
 	}
 }
 
-// DestroyOthers invalidates every session except keep.
-func (s *sessionStore) DestroyOthers(keep string) {
-	if err := s.store.DeleteOtherSessions(hashToken(keep)); err != nil {
-		logf("panel: session: destroy others failed: %v", err)
+// DestroyAll invalidates every session of the user.
+func (s *sessionStore) DestroyAll(userID int64) {
+	if err := s.store.DeleteUserSessions(userID); err != nil {
+		logf("panel: session: destroy all failed: %v", err)
 	}
 }