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/config/config.go

@@ -46,6 +46,22 @@ type User struct {
 	Hash     string    `json:"hash"`
 	Created  time.Time `json:"created"`
 	LastSeen time.Time `json:"last_seen,omitempty"`
+	// Guest marks a temporary login made to show somebody the console: it may only read,
+	// it expires by itself at Expires, and it is not one of the machine's accounts — it is
+	// left out of the account list, does not count towards "the last account", and cannot
+	// be the one an empty user name means. See internal/api/guests.go.
+	Guest bool `json:"guest,omitempty"`
+	// Expires is when a guest login stops working. A guest without one has already
+	// expired, which is the safe way to read a half-written file.
+	Expires time.Time `json:"expires,omitempty"`
+	// IssuedBy is the account that made this guest login.
+	IssuedBy string `json:"issued_by,omitempty"`
+}
+
+// Expired reports whether a guest login's time is up. A real account never expires; a
+// guest with no expiry at all counts as expired rather than as forever.
+func (u User) Expired(now time.Time) bool {
+	return u.Guest && (u.Expires.IsZero() || now.After(u.Expires))
 }
 
 // UpdateSource is where this machine looks for a newer Ham Lab, and how often. The field
@@ -82,8 +98,8 @@ type Config struct {
 	Listen string `json:"listen"`
 	// PasswordHash is the single login of installs before users existed. On load it becomes
 	// the first user (see MigrateUsers) and is then dropped from the file.
-	PasswordHash string `json:"password_hash,omitempty"`
-	Users        []User `json:"users,omitempty"`
+	PasswordHash string  `json:"password_hash,omitempty"`
+	Users        []User  `json:"users,omitempty"`
 	TLS          string  `json:"tls,omitempty"` // "auto" → self-signed cert in the data dir; "" → plain HTTP
 	Tokens       []Token `json:"tokens,omitempty"`
 	Nodes        []Node  `json:"nodes,omitempty"`
@@ -145,6 +161,18 @@ func (c *Config) MigrateUsers(name string) bool {
 	return true
 }
 
+// Accounts is every real account: the machine's users, without the guest logins.
+// Call under View/Update or on a config nobody else holds.
+func (c *Config) Accounts() []User {
+	out := make([]User, 0, len(c.Users))
+	for _, u := range c.Users {
+		if !u.Guest {
+			out = append(out, u)
+		}
+	}
+	return out
+}
+
 // User finds an account by name. Call under View/Update or on a config nobody else holds.
 func (c *Config) User(name string) (User, bool) {
 	for _, u := range c.Users {