client/web: split errTaggedSelf resp from getTailscaleBrowserSession

Previously returned errTaggedSource in the case that of any tagged
source. Now distinguishing whether the source was local or remote.
We'll be presenting the two cases with varying copy on the frontend.

Updates tailscale/corp#14335

Signed-off-by: Sonia Appasamy <sonia@tailscale.com>

client/web/web.go

@@ -291,7 +291,8 @@ func (s *Server) serveLoginAPI(w http.ResponseWriter, r *http.Request) {
 var (
 	errNoSession          = errors.New("no-browser-session")
 	errNotUsingTailscale  = errors.New("not-using-tailscale")
-	errTaggedSource      = errors.New("tagged-source")
+	errTaggedRemoteSource = errors.New("tagged-remote-source")
+	errTaggedLocalSource  = errors.New("tagged-local-source")
 	errNotOwner           = errors.New("not-owner")
 )
 
@@ -304,8 +305,13 @@ var (
 //
 //   - (errNoSession) The request does not have a session.
 //
-//   - (errTaggedSource) The source is a tagged node. Users must use their
-//     own user-owned devices to manage other nodes' web clients.
+//   - (errTaggedRemoteSource) The source is remote (another node) and tagged.
+//     Users must use their own user-owned devices to manage other nodes'
+//     web clients.
+//
+//   - (errTaggedLocalSource) The source is local (the same node) and tagged.
+//     Tagged nodes can only be remotely managed, allowing ACLs to dictate
+//     access to web clients.
 //
 //   - (errNotOwner) The source is not the owner of this client (if the
 //     client is user-owned). Only the owner is allowed to manage the
@@ -318,25 +324,24 @@ var (
 // The WhoIsResponse is always populated, with a non-nil Node and UserProfile,
 // unless getTailscaleBrowserSession reports errNotUsingTailscale.
 func (s *Server) getTailscaleBrowserSession(r *http.Request) (*browserSession, *apitype.WhoIsResponse, error) {
-	whoIs, err := s.lc.WhoIs(r.Context(), r.RemoteAddr)
+	whoIs, whoIsErr := s.lc.WhoIs(r.Context(), r.RemoteAddr)
+	status, statusErr := s.lc.StatusWithoutPeers(r.Context())
 	switch {
-	case err != nil:
+	case whoIsErr != nil:
 		return nil, nil, errNotUsingTailscale
-	case whoIs.Node.IsTagged():
-		return nil, whoIs, errTaggedSource
-	}
-	srcNode := whoIs.Node.ID
-	srcUser := whoIs.UserProfile.ID
-
-	status, err := s.lc.StatusWithoutPeers(r.Context())
-	switch {
-	case err != nil:
-		return nil, whoIs, err
+	case statusErr != nil:
+		return nil, whoIs, statusErr
 	case status.Self == nil:
 		return nil, whoIs, errors.New("missing self node in tailscale status")
-	case !status.Self.IsTagged() && status.Self.UserID != srcUser:
+	case whoIs.Node.IsTagged() && whoIs.Node.StableID == status.Self.ID:
+		return nil, whoIs, errTaggedLocalSource
+	case whoIs.Node.IsTagged():
+		return nil, whoIs, errTaggedRemoteSource
+	case !status.Self.IsTagged() && status.Self.UserID != whoIs.UserProfile.ID:
 		return nil, whoIs, errNotOwner
 	}
+	srcNode := whoIs.Node.ID
+	srcUser := whoIs.UserProfile.ID
 
 	cookie, err := r.Cookie(sessionCookieName)
 	if errors.Is(err, http.ErrNoCookie) {

client/web/web_test.go

@@ -151,15 +151,15 @@ func TestGetTailscaleBrowserSession(t *testing.T) {
 	tags := views.SliceOf([]string{"tag:server"})
 	tailnetNodes := map[string]*apitype.WhoIsResponse{
 		userANodeIP: {
-			Node:        &tailcfg.Node{ID: 1},
+			Node:        &tailcfg.Node{ID: 1, StableID: "1"},
 			UserProfile: userA,
 		},
 		userBNodeIP: {
-			Node:        &tailcfg.Node{ID: 2},
+			Node:        &tailcfg.Node{ID: 2, StableID: "2"},
 			UserProfile: userB,
 		},
 		taggedNodeIP: {
-			Node: &tailcfg.Node{ID: 3, Tags: tags.AsSlice()},
+			Node: &tailcfg.Node{ID: 3, StableID: "3", Tags: tags.AsSlice()},
 		},
 	}
 
@@ -240,11 +240,26 @@ func TestGetTailscaleBrowserSession(t *testing.T) {
 			wantError:   errNotOwner,
 		},
 		{
-			name:        "tagged-source",
+			name:        "tagged-remote-source",
 			selfNode:    &ipnstate.PeerStatus{ID: "self", UserID: userA.ID},
 			remoteAddr:  taggedNodeIP,
 			wantSession: nil,
-			wantError:   errTaggedSource,
+			wantError:   errTaggedRemoteSource,
+		},
+		{
+			name:        "tagged-local-source",
+			selfNode:    &ipnstate.PeerStatus{ID: "3"},
+			remoteAddr:  taggedNodeIP, // same node as selfNode
+			wantSession: nil,
+			wantError:   errTaggedLocalSource,
+		},
+		{
+			name:        "not-tagged-local-source",
+			selfNode:    &ipnstate.PeerStatus{ID: "1", UserID: userA.ID},
+			remoteAddr:  userANodeIP, // same node as selfNode
+			cookie:      userASession.ID,
+			wantSession: userASession,
+			wantError:   nil, // should not error
 		},
 		{
 			name:        "has-session",