A guest login: temporary, look-only, revocable

Users -> Guest logins makes a throwaway user name and password, good for half
an hour by default, to hand to somebody who wants to see the console. It is a
normal account with `guest: true` and an expiry, so login, sessions and the
saved look need no special case, and it is left out of the account list, out of
"the last account can't be removed", and out of the one account an empty user
name means.

What a guest may do is one allow-list, checked in the auth middleware, rather
than a flag ~190 handlers have to remember. The list is matched by asking the
router which handler a request would reach, so it cannot drift from the routes
it names, and it is checked against the scoped path — /api/nodes/grid/procs is
/api/procs on grid — because the hub proxies to a node with a token that is
full control of that node. The node cannot tell a guest from its owner, so the
only place it can be stopped is here, before the request leaves.

A guest gets the dashboard, containers, stacks, disks, hardware, ZFS and usage,
on this machine and on any managed one, and nothing else: no terminal (attaching
is a GET, and it is a root shell), no files, no container logs or environments,
no stack files, no alert channels, no cron, no tokens, no settings, no power.

Expiry is enforced on every request and swept once a minute, so a console left
open on a visitor's phone stops within the minute rather than at their next
click; revoking signs them out at once. The console hides what a guest cannot
use and says how long is left where the power button would be.

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

internal/api/users.go

@@ -26,6 +26,10 @@ type actor struct {
 	Session string // session ID, "" for a token
 	token   string // the raw cookie token, so a handler can spare the current session
 	Token   string // token name, "" for a session
+	// Guest marks a temporary look-around login, and Expires is when it stops working. What
+	// a guest may reach is decided in the middleware, not here; see internal/api/guests.go.
+	Guest   bool
+	Expires time.Time
 }
 
 type ctxKey int
@@ -44,6 +48,8 @@ func actorOf(r *http.Request) actor {
 // who names the caller for a log line: "core@10.0.0.5" for a person, "token:hub:core@…" for a hub.
 func (a actor) String() string {
 	switch {
+	case a.User != "" && a.Guest:
+		return "guest:" + a.User
 	case a.User != "":
 		return a.User
 	case a.Token != "":
@@ -59,7 +65,7 @@ func (s *Server) listUsers(w http.ResponseWriter, r *http.Request) {
 	counts := s.sessions.Count()
 	var out []map[string]any
 	s.cfg.View(func(c *config.Config) {
-		for _, u := range c.Users {
+		for _, u := range c.Accounts() { // guest logins are listed on their own, see listGuests
 			var seen any
 			if !u.LastSeen.IsZero() {
 				seen = u.LastSeen
@@ -84,6 +90,10 @@ func (s *Server) addUser(w http.ResponseWriter, r *http.Request) {
 		jsonErr(w, 400, "a user name is 1–32 lower-case letters, digits, . _ or -, starting with a letter or digit")
 		return
 	}
+	if strings.HasPrefix(name, guestPrefix) {
+		jsonErr(w, 400, "names starting with "+guestPrefix+" belong to guest logins")
+		return
+	}
 	if len(body.Password) < auth.MinPasswordLen {
 		jsonErr(w, 400, "password must be at least 12 characters")
 		return
@@ -141,7 +151,7 @@ func (s *Server) removeUser(w http.ResponseWriter, r *http.Request) {
 	}
 	found, last := false, false
 	if err := s.cfg.Update(func(c *config.Config) {
-		if len(c.Users) <= 1 {
+		if len(c.Accounts()) <= 1 { // guest logins don't keep the last real account alive
 			last = true
 			return
 		}