add SSO session extend flow (management)

Adds the management-server half of the SSO session-extension feature:

- New ExtendAuthSession gRPC RPC that refreshes a peer's session expiry
  using a fresh JWT, validated through the same pipeline as Login but
  without tearing down the tunnel or redoing the NetworkMap sync.
- Per-peer SessionExpiresAt timestamp on every LoginResponse and
  SyncResponse so connected clients learn the deadline on the existing
  long-lived stream, and admin-side changes (toggling expiration,
  changing the expiration window) reach every peer within seconds.
- SessionExpiresAt(...) helper on Peer that derives the absolute UTC
  deadline from LastLogin + the account-level PeerLoginExpiration
  setting, returning zero when the peer is not SSO-tracked or expiration
  is disabled.

The matching client-side consumer of these fields lands separately.

shared/management/proto/management.proto

@@ -52,6 +52,14 @@ service ManagementService {
   // Executes a job on a target peer (e.g., debug bundle)
   rpc Job(stream EncryptedMessage) returns (stream EncryptedMessage) {}
 
+  // ExtendAuthSession refreshes the peer's session expiry deadline using a fresh JWT.
+  // Same JWT validation pipeline as Login (including jwt.UserID == peer.UserID check),
+  // but does not redo the network-map sync. Only valid for SSO-registered peers where
+  // login expiration is enabled. The tunnel remains up.
+  // EncryptedMessage of the request has a body of ExtendAuthSessionRequest.
+  // EncryptedMessage of the response has a body of ExtendAuthSessionResponse.
+  rpc ExtendAuthSession(EncryptedMessage) returns (EncryptedMessage) {}
+
   // CreateExpose creates a temporary reverse proxy service for a peer
   rpc CreateExpose(EncryptedMessage) returns (EncryptedMessage) {}
 
@@ -133,6 +141,12 @@ message SyncResponse {
 
   // Posture checks to be evaluated by client
   repeated Checks Checks = 6;
+
+  // Absolute UTC instant at which the peer's SSO session expires.
+  // Unset when the peer is not SSO-registered or login expiration is disabled.
+  // Carried on every Sync snapshot so admin-side changes propagate live without
+  // a client reconnect.
+  google.protobuf.Timestamp sessionExpiresAt = 7;
 }
 
 message  SyncMetaRequest {
@@ -244,6 +258,26 @@ message LoginResponse {
   PeerConfig peerConfig = 2;
   // Posture checks to be evaluated by client
   repeated Checks Checks = 3;
+
+  // Absolute UTC instant at which the peer's SSO session expires.
+  // Unset when the peer is not SSO-registered or login expiration is disabled.
+  google.protobuf.Timestamp sessionExpiresAt = 4;
+}
+
+// ExtendAuthSessionRequest carries a fresh JWT to refresh the peer's session deadline.
+// The encrypted body of an EncryptedMessage with this payload is sent to the
+// ExtendAuthSession RPC.
+message ExtendAuthSessionRequest {
+  // SSO token (must be a fresh, valid JWT for the peer's owning user)
+  string jwtToken = 1;
+  // Meta data of the peer (used for IdP user info refresh consistent with Login)
+  PeerSystemMeta meta = 2;
+}
+
+// ExtendAuthSessionResponse contains the refreshed session deadline.
+message ExtendAuthSessionResponse {
+  // Absolute UTC instant at which the peer's SSO session now expires.
+  google.protobuf.Timestamp sessionExpiresAt = 1;
 }
 
 message ServerKeyResponse {

shared/management/proto/management_grpc.pb.go

@@ -52,6 +52,13 @@ type ManagementServiceClient interface {
 	Logout(ctx context.Context, in *EncryptedMessage, opts ...grpc.CallOption) (*Empty, error)
 	// Executes a job on a target peer (e.g., debug bundle)
 	Job(ctx context.Context, opts ...grpc.CallOption) (ManagementService_JobClient, error)
+	// ExtendAuthSession refreshes the peer's session expiry deadline using a fresh JWT.
+	// Same JWT validation pipeline as Login (including jwt.UserID == peer.UserID check),
+	// but does not redo the network-map sync. Only valid for SSO-registered peers where
+	// login expiration is enabled. The tunnel remains up.
+	// EncryptedMessage of the request has a body of ExtendAuthSessionRequest.
+	// EncryptedMessage of the response has a body of ExtendAuthSessionResponse.
+	ExtendAuthSession(ctx context.Context, in *EncryptedMessage, opts ...grpc.CallOption) (*EncryptedMessage, error)
 	// CreateExpose creates a temporary reverse proxy service for a peer
 	CreateExpose(ctx context.Context, in *EncryptedMessage, opts ...grpc.CallOption) (*EncryptedMessage, error)
 	// RenewExpose extends the TTL of an active expose session
@@ -194,6 +201,15 @@ func (x *managementServiceJobClient) Recv() (*EncryptedMessage, error) {
 	return m, nil
 }
 
+func (c *managementServiceClient) ExtendAuthSession(ctx context.Context, in *EncryptedMessage, opts ...grpc.CallOption) (*EncryptedMessage, error) {
+	out := new(EncryptedMessage)
+	err := c.cc.Invoke(ctx, "/management.ManagementService/ExtendAuthSession", in, out, opts...)
+	if err != nil {
+		return nil, err
+	}
+	return out, nil
+}
+
 func (c *managementServiceClient) CreateExpose(ctx context.Context, in *EncryptedMessage, opts ...grpc.CallOption) (*EncryptedMessage, error) {
 	out := new(EncryptedMessage)
 	err := c.cc.Invoke(ctx, "/management.ManagementService/CreateExpose", in, out, opts...)
@@ -259,6 +275,13 @@ type ManagementServiceServer interface {
 	Logout(context.Context, *EncryptedMessage) (*Empty, error)
 	// Executes a job on a target peer (e.g., debug bundle)
 	Job(ManagementService_JobServer) error
+	// ExtendAuthSession refreshes the peer's session expiry deadline using a fresh JWT.
+	// Same JWT validation pipeline as Login (including jwt.UserID == peer.UserID check),
+	// but does not redo the network-map sync. Only valid for SSO-registered peers where
+	// login expiration is enabled. The tunnel remains up.
+	// EncryptedMessage of the request has a body of ExtendAuthSessionRequest.
+	// EncryptedMessage of the response has a body of ExtendAuthSessionResponse.
+	ExtendAuthSession(context.Context, *EncryptedMessage) (*EncryptedMessage, error)
 	// CreateExpose creates a temporary reverse proxy service for a peer
 	CreateExpose(context.Context, *EncryptedMessage) (*EncryptedMessage, error)
 	// RenewExpose extends the TTL of an active expose session
@@ -299,6 +322,9 @@ func (UnimplementedManagementServiceServer) Logout(context.Context, *EncryptedMe
 func (UnimplementedManagementServiceServer) Job(ManagementService_JobServer) error {
 	return status.Errorf(codes.Unimplemented, "method Job not implemented")
 }
+func (UnimplementedManagementServiceServer) ExtendAuthSession(context.Context, *EncryptedMessage) (*EncryptedMessage, error) {
+	return nil, status.Errorf(codes.Unimplemented, "method ExtendAuthSession not implemented")
+}
 func (UnimplementedManagementServiceServer) CreateExpose(context.Context, *EncryptedMessage) (*EncryptedMessage, error) {
 	return nil, status.Errorf(codes.Unimplemented, "method CreateExpose not implemented")
 }
@@ -494,6 +520,24 @@ func (x *managementServiceJobServer) Recv() (*EncryptedMessage, error) {
 	return m, nil
 }
 
+func _ManagementService_ExtendAuthSession_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
+	in := new(EncryptedMessage)
+	if err := dec(in); err != nil {
+		return nil, err
+	}
+	if interceptor == nil {
+		return srv.(ManagementServiceServer).ExtendAuthSession(ctx, in)
+	}
+	info := &grpc.UnaryServerInfo{
+		Server:     srv,
+		FullMethod: "/management.ManagementService/ExtendAuthSession",
+	}
+	handler := func(ctx context.Context, req interface{}) (interface{}, error) {
+		return srv.(ManagementServiceServer).ExtendAuthSession(ctx, req.(*EncryptedMessage))
+	}
+	return interceptor(ctx, in, info, handler)
+}
+
 func _ManagementService_CreateExpose_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
 	in := new(EncryptedMessage)
 	if err := dec(in); err != nil {
@@ -583,6 +627,10 @@ var ManagementService_ServiceDesc = grpc.ServiceDesc{
 			MethodName: "Logout",
 			Handler:    _ManagementService_Logout_Handler,
 		},
+		{
+			MethodName: "ExtendAuthSession",
+			Handler:    _ManagementService_ExtendAuthSession_Handler,
+		},
 		{
 			MethodName: "CreateExpose",
 			Handler:    _ManagementService_CreateExpose_Handler,