mcp: add global runtime flag (#5604)

## Summary

Adds global runtime flag to enable/disable MCP support. (off by
default).

```yaml
runtime_flags:
  mcp: true
```

## Related issues

Fix:
https://linear.app/pomerium/issue/ENG-2367/place-mcp-support-behind-a-runtime-flag

## User Explanation

<!-- How would you explain this change to the user? If this
change doesn't create any user-facing changes, you can leave
this blank. If filled out, add the `docs` label -->

## Checklist

- [x] reference any related issues
- [ ] updated unit tests
- [ ] add appropriate label (`enhancement`, `bug`, `breaking`,
`dependencies`, `ci`)
- [ ] ready for review

authorize/check_response.go

@@ -21,6 +21,7 @@ import (
 
 	"github.com/pomerium/pomerium/authorize/checkrequest"
 	"github.com/pomerium/pomerium/authorize/evaluator"
+	"github.com/pomerium/pomerium/config"
 	"github.com/pomerium/pomerium/internal/httputil"
 	"github.com/pomerium/pomerium/internal/log"
 	"github.com/pomerium/pomerium/internal/urlutil"
@@ -358,9 +359,11 @@ func (a *Authorize) userInfoEndpointURL(in *envoy_service_auth_v3.CheckRequest)
 }
 
 func (a *Authorize) shouldRedirect(in *envoy_service_auth_v3.CheckRequest, request *evaluator.Request) bool {
+	if a.currentConfig.Load().Options.IsRuntimeFlagSet(config.RuntimeFlagMCP) {
 		if request.Policy.IsMCPServer() {
 			return false
 		}
+	}
 
 	requestHeaders := in.GetAttributes().GetRequest().GetHttp().GetHeaders()
 	if requestHeaders == nil {

authorize/check_response_test.go

@@ -113,7 +113,8 @@ func TestAuthorize_handleResult(t *testing.T) {
 		assert.NoError(t, err)
 		assert.Equal(t, 495, int(res.GetDeniedResponse().GetStatus().GetCode()))
 	})
-	t.Run("mcp-route-unauthenticated", func(t *testing.T) {
+	t.Run("mcp-route-unauthenticated, mcp flag is on", func(t *testing.T) {
+		opt.RuntimeFlags[config.RuntimeFlagMCP] = true
 		res, err := a.handleResult(context.Background(),
 			&envoy_service_auth_v3.CheckRequest{},
 			&evaluator.Request{
@@ -125,6 +126,19 @@ func TestAuthorize_handleResult(t *testing.T) {
 		assert.NoError(t, err)
 		assert.Equal(t, 401, int(res.GetDeniedResponse().GetStatus().GetCode()))
 	})
+	t.Run("mcp-route-unauthenticated, mcp flag is off", func(t *testing.T) {
+		opt.RuntimeFlags[config.RuntimeFlagMCP] = false
+		res, err := a.handleResult(context.Background(),
+			&envoy_service_auth_v3.CheckRequest{},
+			&evaluator.Request{
+				Policy: &config.Policy{MCP: &config.MCP{}},
+			},
+			&evaluator.Result{
+				Allow: evaluator.NewRuleResult(false, criteria.ReasonUserUnauthenticated),
+			})
+		assert.NoError(t, err)
+		assert.Equal(t, 302, int(res.GetDeniedResponse().GetStatus().GetCode()))
+	})
 }
 
 func TestAuthorize_okResponse(t *testing.T) {

authorize/grpc.go

@@ -123,6 +123,7 @@ func (a *Authorize) maybeGetSessionFromRequest(
 	hreq *http.Request,
 	policy *config.Policy,
 ) (*session.Session, error) {
+	if a.currentConfig.Load().Options.IsRuntimeFlagSet(config.RuntimeFlagMCP) {
 		if policy.IsMCPServer() {
 			s, err := a.getMCPSession(ctx, hreq)
 			if err != nil {
@@ -131,6 +132,7 @@ func (a *Authorize) maybeGetSessionFromRequest(
 			}
 			return s, nil
 		}
+	}
 
 	// attempt to create a session from an incoming idp token
 	return config.NewIncomingIDPTokenSessionCreator(

authorize/state.go

@@ -59,13 +59,17 @@ func newAuthorizeStateFromConfig(
 		previousEvaluator = previousState.evaluator
 	}
 
+	var evaluatorOptions []evaluator.Option
+	if cfg.Options.IsRuntimeFlagSet(config.RuntimeFlagMCP) {
 		mcp, err := mcp.New(ctx, mcp.DefaultPrefix, cfg)
 		if err != nil {
 			return nil, fmt.Errorf("authorize: failed to create mcp handler: %w", err)
 		}
 		state.mcp = mcp
+		evaluatorOptions = append(evaluatorOptions, evaluator.WithMCPAccessTokenProvider(mcp))
+	}
 
-	state.evaluator, err = newPolicyEvaluator(ctx, cfg.Options, store, previousEvaluator, evaluator.WithMCPAccessTokenProvider(mcp))
+	state.evaluator, err = newPolicyEvaluator(ctx, cfg.Options, store, previousEvaluator, evaluatorOptions...)
 	if err != nil {
 		return nil, fmt.Errorf("authorize: failed to update policy with options: %w", err)
 	}

config/envoyconfig/routes.go

@@ -72,7 +72,7 @@ func (b *Builder) buildPomeriumHTTPRoutes(
 		)
 
 		// Only add oauth-authorization-server route if there's an MCP policy for this host
-		if isMCPHost {
+		if options.IsRuntimeFlagSet(config.RuntimeFlagMCP) && isMCPHost {
 			routes = append(routes, b.buildControlPlanePathRoute(options, "/.well-known/oauth-authorization-server"))
 		}
 	}

config/envoyconfig/routes_test.go

@@ -2331,7 +2331,9 @@ func Test_buildPomeriumHTTPRoutesWithMCP(t *testing.T) {
 					MCP:  &config.MCP{}, // This marks the policy as an MCP policy
 				},
 			},
+			RuntimeFlags: config.DefaultRuntimeFlags(),
 		}
+		options.RuntimeFlags[config.RuntimeFlagMCP] = true
 
 		routes, err := b.buildPomeriumHTTPRoutes(options, "example.com", true)
 		require.NoError(t, err)
@@ -2347,4 +2349,38 @@ func Test_buildPomeriumHTTPRoutesWithMCP(t *testing.T) {
 			`+routeString("path", "/.well-known/oauth-authorization-server")+`
 		]`, routes)
 	})
+
+	t.Run("with MCP policy, runtime flag is off", func(t *testing.T) {
+		b := &Builder{filemgr: filemgr.NewManager()}
+		options := &config.Options{
+			Services:              "all",
+			AuthenticateURLString: "https://authenticate.example.com",
+			Policies: []config.Policy{
+				{
+					From: "https://example.com",
+					To:   mustParseWeightedURLs(t, "https://to.example.com"),
+				},
+				{
+					From: "https://mcp.example.com",
+					To:   mustParseWeightedURLs(t, "https://mcp-backend.example.com"),
+					MCP:  &config.MCP{}, // This marks the policy as an MCP policy
+				},
+			},
+			RuntimeFlags: config.DefaultRuntimeFlags(),
+		}
+		options.RuntimeFlags[config.RuntimeFlagMCP] = false
+
+		routes, err := b.buildPomeriumHTTPRoutes(options, "example.com", true)
+		require.NoError(t, err)
+
+		// Verify the expected route structures
+		testutil.AssertProtoJSONEqual(t, `[
+			`+routeString("path", "/ping")+`,
+			`+routeString("path", "/healthz")+`,
+			`+routeString("path", "/.pomerium")+`,
+			`+routeString("prefix", "/.pomerium/")+`,
+			`+routeString("path", "/.well-known/pomerium")+`,
+			`+routeString("prefix", "/.well-known/pomerium/")+`
+		]`, routes)
+	})
 }

config/runtime_flags.go

@@ -29,6 +29,9 @@ var (
 	// RuntimeFlagAuthorizeUseSyncedData enables synced data for querying the databroker for
 	// certain types of data.
 	RuntimeFlagAuthorizeUseSyncedData = runtimeFlag("authorize_use_synced_data", true)
+
+	// RuntimeFlagMCP enables the MCP services for the authorize service
+	RuntimeFlagMCP = runtimeFlag("mcp", false)
 )
 
 // RuntimeFlag is a runtime flag that can flip on/off certain features

internal/controlplane/http.go

@@ -81,9 +81,11 @@ func (srv *Server) mountCommonEndpoints(root *mux.Router, cfg *config.Config) er
 	root.Path("/.well-known/pomerium/jwks.json").Methods(http.MethodGet).Handler(traceHandler(handlers.JWKSHandler(signingKey)))
 	root.Path(urlutil.HPKEPublicKeyPath).Methods(http.MethodGet).Handler(traceHandler(hpke_handlers.HPKEPublicKeyHandler(hpkePublicKey)))
 
+	if cfg.Options.IsRuntimeFlagSet(config.RuntimeFlagMCP) {
 		root.Path("/.well-known/oauth-authorization-server").
 			Methods(http.MethodGet, http.MethodOptions).
 			Handler(mcp.AuthorizationServerMetadataHandler(mcp.DefaultPrefix))
+	}
 
 	return nil
 }

proxy/handlers.go

@@ -24,8 +24,10 @@ func (p *Proxy) registerDashboardHandlers(r *mux.Router, opts *config.Options) *
 	h := httputil.DashboardSubrouter(r)
 	h.Use(middleware.SetHeaders(httputil.HeadersContentSecurityPolicy))
 
+	if opts.IsRuntimeFlagSet(config.RuntimeFlagMCP) {
 		// model context protocol
 		h.PathPrefix("/mcp").Handler(p.mcp.Load().HandlerFunc())
+	}
 
 	// special pomerium endpoints for users to view their session
 	h.Path("/").Handler(httputil.HandlerFunc(p.userInfo)).Methods(http.MethodGet)

proxy/proxy.go

@@ -76,18 +76,19 @@ func New(ctx context.Context, cfg *config.Config) (*Proxy, error) {
 		return nil, err
 	}
 
-	mcp, err := mcp.New(ctx, mcp.DefaultPrefix, cfg)
-	if err != nil {
-		return nil, fmt.Errorf("proxy: failed to create mcp handler: %w", err)
-	}
-
 	p := &Proxy{
 		tracerProvider: tracerProvider,
 		state:          atomicutil.NewValue(state),
 		currentConfig:  atomicutil.NewValue(&config.Config{Options: config.NewDefaultOptions()}),
 		currentRouter:  atomicutil.NewValue(httputil.NewRouter()),
 		logoProvider:   portal.NewLogoProvider(),
-		mcp:            atomicutil.NewValue(mcp),
+	}
+	if cfg.Options.IsRuntimeFlagSet(config.RuntimeFlagMCP) {
+		mcp, err := mcp.New(ctx, mcp.DefaultPrefix, cfg)
+		if err != nil {
+			return nil, fmt.Errorf("proxy: failed to create mcp handler: %w", err)
+		}
+		p.mcp = atomicutil.NewValue(mcp)
 	}
 	p.OnConfigChange(ctx, cfg)
 	p.webauthn = webauthn.New(p.getWebauthnState)
@@ -110,12 +111,14 @@ func (p *Proxy) OnConfigChange(ctx context.Context, cfg *config.Config) {
 		return
 	}
 
+	if cfg.Options.IsRuntimeFlagSet(config.RuntimeFlagMCP) {
 		mcp, err := mcp.New(ctx, mcp.DefaultPrefix, cfg)
 		if err != nil {
 			log.Ctx(ctx).Error().Err(err).Msg("proxy: failed to update proxy state from configuration settings")
 		} else {
 			p.mcp.Store(mcp)
 		}
+	}
 
 	p.currentConfig.Store(cfg)
 	if err := p.setHandlers(ctx, cfg.Options); err != nil {