[client] Force interactive login when extending the auth session

A session extend must be answered from the account the peer is registered
under. With a silent PKCE flow (DisablePromptLogin or max_age=0) the IdP
answers from whatever session it already holds, which need not be the
peer's account when several are signed in; the token then fails the
user match in ExtendAuthSession with no way to pick another account.

Mark the PKCE flow request as a session extend so the management server
can force prompt=login for it, overriding the configured silent flow.

management/internals/shared/grpc/pkce_flow_test.go

@@ -0,0 +1,75 @@
+package grpc
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"github.com/netbirdio/netbird/shared/management/client/common"
+	"github.com/netbirdio/netbird/shared/management/proto"
+)
+
+func TestApplySessionExtendFlowPolicy(t *testing.T) {
+	tests := []struct {
+		name               string
+		flow               *proto.PKCEAuthorizationFlow
+		sessionExtend      bool
+		disablePromptLogin bool
+		loginFlag          uint32
+	}{
+		{
+			name: "extend forces prompt=login over a silent flow",
+			flow: &proto.PKCEAuthorizationFlow{
+				ProviderConfig: &proto.ProviderConfig{
+					DisablePromptLogin: true,
+					LoginFlag:          uint32(common.LoginFlagMaxAge0),
+				},
+			},
+			sessionExtend:      true,
+			disablePromptLogin: false,
+			loginFlag:          uint32(common.LoginFlagPromptLogin),
+		},
+		{
+			name: "extend replaces max_age=0 so login_hint is honoured",
+			flow: &proto.PKCEAuthorizationFlow{
+				ProviderConfig: &proto.ProviderConfig{
+					DisablePromptLogin: false,
+					LoginFlag:          uint32(common.LoginFlagMaxAge0),
+				},
+			},
+			sessionExtend:      true,
+			disablePromptLogin: false,
+			loginFlag:          uint32(common.LoginFlagPromptLogin),
+		},
+		{
+			name: "login keeps the configured flow untouched",
+			flow: &proto.PKCEAuthorizationFlow{
+				ProviderConfig: &proto.ProviderConfig{
+					DisablePromptLogin: true,
+					LoginFlag:          uint32(common.LoginFlagMaxAge0),
+				},
+			},
+			sessionExtend:      false,
+			disablePromptLogin: true,
+			loginFlag:          uint32(common.LoginFlagMaxAge0),
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			applySessionExtendFlowPolicy(tc.flow, tc.sessionExtend)
+			cfg := tc.flow.GetProviderConfig()
+			assert.Equal(t, tc.disablePromptLogin, cfg.GetDisablePromptLogin())
+			assert.Equal(t, tc.loginFlag, cfg.GetLoginFlag())
+		})
+	}
+}
+
+// A provider config is not guaranteed to be present on the response; clearing
+// the flag must not panic when the validator returned an empty flow.
+func TestApplySessionExtendFlowPolicyWithoutProviderConfig(t *testing.T) {
+	assert.NotPanics(t, func() {
+		applySessionExtendFlowPolicy(&proto.PKCEAuthorizationFlow{}, true)
+		applySessionExtendFlowPolicy(nil, true)
+	})
+}

management/internals/shared/grpc/server.go

@@ -1180,7 +1180,8 @@ func (s *Server) GetPKCEAuthorizationFlow(ctx context.Context, req *proto.Encryp
 		return nil, status.Errorf(codes.Internal, "failed to get server key")
 	}
 
-	err = encryption.DecryptMessage(peerKey, key, req.Body, &proto.PKCEAuthorizationFlowRequest{})
+	flowReq := &proto.PKCEAuthorizationFlowRequest{}
+	err = encryption.DecryptMessage(peerKey, key, req.Body, flowReq)
 	if err != nil {
 		errMSG := fmt.Sprintf("error while decrypting peer's message with Wireguard public key %s.", req.WgPubKey)
 		log.WithContext(ctx).Warn(errMSG)
@@ -1224,6 +1225,7 @@ func (s *Server) GetPKCEAuthorizationFlow(ctx context.Context, req *proto.Encryp
 	}
 
 	flowInfoResp := s.integratedPeerValidator.ValidateFlowResponse(ctx, peerKey.String(), initInfoFlow)
+	applySessionExtendFlowPolicy(flowInfoResp, flowReq.GetSessionExtend())
 
 	encryptedResp, err := encryption.EncryptMessage(peerKey, key, flowInfoResp)
 	if err != nil {
@@ -1236,6 +1238,32 @@ func (s *Server) GetPKCEAuthorizationFlow(ctx context.Context, req *proto.Encryp
 	}, nil
 }
 
+// applySessionExtendFlowPolicy forces a prompt=login flow for a session extend.
+//
+// An extend renews the session of one specific peer, so its token has to come
+// from the account that peer is registered under. A flow that does not prompt
+// leaves the choice to the IdP, which answers a silent authorization from any
+// session it already holds — not necessarily this peer's account when several
+// are signed in, and login_hint is a suggestion the IdP may ignore. The token
+// then fails the jwt.UserID == peer.UserID check in ExtendAuthSession, and the
+// user is given no opportunity to pick a different account.
+//
+// LoginFlagPromptLogin rather than max_age=0: both re-authenticate, but with
+// prompt=login the IdP honours login_hint and offers the peer's own account,
+// whereas max_age=0 leaves the user to find it among every account signed in.
+//
+// Called after ValidateFlowResponse so that a per-peer override cannot reinstate
+// the silent flow for an extend.
+func applySessionExtendFlowPolicy(flow *proto.PKCEAuthorizationFlow, sessionExtend bool) {
+	if !sessionExtend {
+		return
+	}
+	if cfg := flow.GetProviderConfig(); cfg != nil {
+		cfg.DisablePromptLogin = false
+		cfg.LoginFlag = uint32(common.LoginFlagPromptLogin)
+	}
+}
+
 // SyncMeta endpoint is used to synchronize peer's system metadata and notifies the connected,
 // peer's under the same account of any updates.
 func (s *Server) SyncMeta(ctx context.Context, req *proto.EncryptedMessage) (*proto.Empty, error) {