MCP access part 1: update app definition and config

Author: greedy52

api/proto/teleport/legacy/types/types.proto

@@ -1118,6 +1118,24 @@ message AppSpecV3 {
   // want the app to be accessible from any of them. If `public_addr` is explicitly set in the app spec,
   // setting this value to true will overwrite that public address in the web UI.
   bool UseAnyProxyPublicAddr = 14 [(gogoproto.jsontag) = "use_any_proxy_public_addr,omitempty"];
+  // MCP contains MCP server related configurations.
+  MCP MCP = 15 [(gogoproto.jsontag) = "mcp,omitempty"];
+}
+
+// MCP contains MCP server-related configurations.
+message MCP {
+  // Command to launch stdio-based MCP servers.
+  string command = 1;
+  // Args to execute with the command.
+  repeated string args = 2;
+  // RunAsLocalUser is the local user account under which the command will be
+  // executed. Required for stdio-based MCP servers.
+  string run_as_local_user = 3;
+  // StopSignal specifies the OS signal to send for gracefully stopping the
+  // process. If not set, defaults to 0x2 (SIGINT) as it is a common signal for
+  // stopping programs listening on stdin. Signal 0x9 (SIGKILL) is sent
+  // automatically after 10 seconds if the process has not exited.
+  uint32 stop_signal = 4;
 }
 
 // Rewrite is a list of rewriting rules to apply to requests and responses.

api/types/app.go

@@ -70,6 +70,8 @@ type Application interface {
 	IsGCP() bool
 	// IsTCP returns true if this app represents a TCP endpoint.
 	IsTCP() bool
+	// IsMCP returns true if this app represents a MCP server.
+	IsMCP() bool
 	// GetProtocol returns the application protocol.
 	GetProtocol() string
 	// GetAWSAccountID returns value of label containing AWS account ID on this app.
@@ -101,6 +103,8 @@ type Application interface {
 	SetTCPPorts([]*PortRange)
 	// GetIdentityCenter fetches identity center info for the app, if any.
 	GetIdentityCenter() *AppIdentityCenter
+	// GetMCP fetches MCP specific configuration.
+	GetMCP() *MCP
 }
 
 // NewAppV3 creates a new app resource.
@@ -286,10 +290,20 @@ func (a *AppV3) IsTCP() bool {
 	return IsAppTCP(a.Spec.URI)
 }
 
+// IsMCP returns true if this app represents a TCP endpoint.
+func (a *AppV3) IsMCP() bool {
+	return IsAppMCP(a.Spec.URI)
+}
+
 func IsAppTCP(uri string) bool {
 	return strings.HasPrefix(uri, "tcp://")
 }
 
+// IsAppMCP returns true if provided uri is an MCP app.
+func IsAppMCP(uri string) bool {
+	return GetMCPServerTransportType(uri) != ""
+}
+
 // GetProtocol returns the application protocol.
 func (a *AppV3) GetProtocol() string {
 	if a.IsTCP() {
@@ -400,6 +414,11 @@ func (a *AppV3) CheckAndSetDefaults() error {
 			return trace.BadParameter("app %q invalid label key: %q", a.GetName(), key)
 		}
 	}
+
+	if a.Spec.MCP != nil && a.Spec.MCP.Command != "" {
+		a.Spec.URI = SchemaMCPStdio
+	}
+
 	if a.Spec.URI == "" {
 		if a.Spec.Cloud != "" {
 			a.Spec.URI = fmt.Sprintf("cloud://%v", a.Spec.Cloud)
@@ -453,6 +472,13 @@ func (a *AppV3) CheckAndSetDefaults() error {
 		}
 	}
 
+	if a.IsMCP() {
+		a.SetSubKind(SubKindMCP)
+		if err := a.checkMCP(); err != nil {
+			return trace.Wrap(err)
+		}
+	}
+
 	return nil
 }
 
@@ -486,6 +512,28 @@ func (a *AppV3) checkTCPPorts() error {
 	return nil
 }
 
+func (a *AppV3) checkMCP() error {
+	switch {
+	case strings.HasPrefix(a.Spec.URI, SchemaMCPStdio):
+		return trace.Wrap(a.checkMCPStdio())
+	default:
+		return trace.BadParameter("app %q has unsupported MCP URI format", a.GetName())
+	}
+}
+
+func (a *AppV3) checkMCPStdio() error {
+	if a.Spec.MCP == nil {
+		return trace.BadParameter("MCP server %q missing mcp spec", a.GetName())
+	}
+	if a.Spec.MCP.Command == "" {
+		return trace.BadParameter("MCP server %q missing command", a.GetName())
+	}
+	if a.Spec.MCP.RunAsLocalUser == "" {
+		return trace.BadParameter("MCP server %q missing run_as_local_user", a.GetName())
+	}
+	return nil
+}
+
 // GetIdentityCenter returns the Identity Center information for the app, if any.
 // May be nil.
 func (a *AppV3) GetIdentityCenter() *AppIdentityCenter {
@@ -511,6 +559,11 @@ func (a *AppV3) IsEqual(i Application) bool {
 	return false
 }
 
+// GetMCP returns MCP specific configuration.
+func (a *AppV3) GetMCP() *MCP {
+	return a.Spec.MCP
+}
+
 // DeduplicateApps deduplicates apps by combination of app name and public address.
 // Apps can have the same name but also could have different addresses.
 func DeduplicateApps(apps []Application) (result []Application) {
@@ -596,3 +649,15 @@ func (p *PortRange) String() string {
 		return fmt.Sprintf("%d-%d", p.Port, p.EndPort)
 	}
 }
+
+// GetMCPServerTransportType returns the transport of the MCP server based on
+// the URI. If no MCP transport type can be deferred from the URI, an empty
+// string is returned.
+func GetMCPServerTransportType(uri string) string {
+	switch {
+	case strings.HasPrefix(uri, SchemaMCPStdio):
+		return MCPTransportStdio
+	default:
+		return ""
+	}
+}

api/types/app_test.go

@@ -603,6 +603,60 @@ func TestNewAppV3(t *testing.T) {
 			want:    nil,
 			wantErr: require.Error,
 		},
+		{
+			name: "mcp with command",
+			meta: Metadata{
+				Name: "mcp-everything",
+			},
+			spec: AppSpecV3{
+				MCP: &MCP{
+					Command:        "docker",
+					Args:           []string{"run", "-i", "--rm", "mcp/everything"},
+					RunAsLocalUser: "docker",
+				},
+			},
+			want: &AppV3{
+				Kind:    "app",
+				SubKind: "mcp",
+				Version: "v3",
+				Metadata: Metadata{
+					Name:      "mcp-everything",
+					Namespace: "default",
+				},
+				Spec: AppSpecV3{
+					URI: "mcp+stdio://",
+					MCP: &MCP{
+						Command:        "docker",
+						Args:           []string{"run", "-i", "--rm", "mcp/everything"},
+						RunAsLocalUser: "docker",
+					},
+				},
+			},
+			wantErr: require.NoError,
+		},
+		{
+			name: "mcp missing spec",
+			meta: Metadata{
+				Name: "mcp-missing-run-as",
+			},
+			spec: AppSpecV3{
+				URI: "mcp+stdio://",
+			},
+			wantErr: require.Error,
+		},
+		{
+			name: "mcp missing run_as_local_user",
+			meta: Metadata{
+				Name: "mcp-missing-spec",
+			},
+			spec: AppSpecV3{
+				MCP: &MCP{
+					Command: "docker",
+					Args:    []string{"run", "-i", "--rm", "mcp/everything"},
+				},
+			},
+			wantErr: require.Error,
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
@@ -658,3 +712,27 @@ func hasErrAndContains(msg string) require.ErrorAssertionFunc {
 		require.ErrorContains(t, err, msg, msgAndArgs...)
 	}
 }
+
+func TestGetMCPServerTransportType(t *testing.T) {
+	tests := []struct {
+		name string
+		uri  string
+		want string
+	}{
+		{
+			name: "stdio",
+			uri:  "mcp+stdio://",
+			want: MCPTransportStdio,
+		},
+		{
+			name: "unknown",
+			uri:  "http://localhost",
+			want: "",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			require.Equal(t, tt.want, GetMCPServerTransportType(tt.uri))
+		})
+	}
+}

api/types/constants.go

@@ -183,6 +183,14 @@ const (
 	// KindApp is a web app resource.
 	KindApp = "app"
 
+	// SubKindMCP represents an MCP server as a subkind of app.
+	SubKindMCP = KindMCP
+
+	// KindMCP is an MCP server resource.
+	// Currently, MCP servers are accessed through apps.
+	// In the future, they may become a standalone resource kind.
+	KindMCP = "mcp"
+
 	// KindDatabaseServer is a database proxy server resource.
 	KindDatabaseServer = "db_server"
 
@@ -889,6 +897,11 @@ const (
 	// CloudGCP identifies that a resource was discovered in GCP.
 	CloudGCP = "GCP"
 
+	// SchemaMCPStdio is a URI schema for MCP servers using stdio transport.
+	SchemaMCPStdio = "mcp+stdio://"
+	// MCPTransportStdio indicates the MCP server uses stdio transport.
+	MCPTransportStdio = "stdio"
+
 	// DiscoveredResourceNode identifies a discovered SSH node.
 	DiscoveredResourceNode = "node"
 	// DiscoveredResourceDatabase identifies a discovered database.