Allow CORS on discovery endpoint

cmd/dex/config.go

@@ -102,6 +102,7 @@ type Web struct {
 	HTTPS                   string   `json:"https"`
 	TLSCert                 string   `json:"tlsCert"`
 	TLSKey                  string   `json:"tlsKey"`
+	DiscoveryAllowedOrigins []string `json:"discoveryAllowedOrigins"`
 }
 
 // GRPC is the config for the gRPC API.

cmd/dex/serve.go

@@ -179,6 +179,9 @@ func serve(cmd *cobra.Command, args []string) error {
 	if c.OAuth2.SkipApprovalScreen {
 		logger.Infof("config skipping approval screen")
 	}
+	if len(c.Web.DiscoveryAllowedOrigins) > 0 {
+		logger.Infof("config discovery allowed origins: %s", c.Web.DiscoveryAllowedOrigins)
+	}
 
 	// explicitly convert to UTC.
 	now := func() time.Time { return time.Now().UTC() }
@@ -186,6 +189,7 @@ func serve(cmd *cobra.Command, args []string) error {
 	serverConfig := server.Config{
 		SupportedResponseTypes:  c.OAuth2.ResponseTypes,
 		SkipApprovalScreen:      c.OAuth2.SkipApprovalScreen,
+		DiscoveryAllowedOrigins: c.Web.DiscoveryAllowedOrigins,
 		Issuer:                  c.Issuer,
 		Connectors:              connectors,
 		Storage:                 s,

glide.lock

@@ -18,6 +18,8 @@ imports:
   - protoc-gen-go
 - name: github.com/gorilla/context
   version: aed02d124ae4a0e94fea4541c8effd05bf0c8296
+- name: github.com/gorilla/handlers
+  version: 3a5767ca75ece5f7f1440b1d16975247f8d8b221
 - name: github.com/gorilla/mux
   version: 9fa818a44c2bf1396a17f9d5a3c0f6dd39d2ff8e
 - name: github.com/gtank/cryptopasta

glide.yaml

@@ -53,6 +53,8 @@ import:
   version: 9fa818a44c2bf1396a17f9d5a3c0f6dd39d2ff8e
 - package: github.com/gorilla/context
   version: aed02d124ae4a0e94fea4541c8effd05bf0c8296
+- package: github.com/gorilla/handlers
+  version: 3a5767ca75ece5f7f1440b1d16975247f8d8b221
 
 # Package with a bunch of sane crypto defaults. Consider just
 # copy the code (as recommended by the repo itself) instead

server/handlers.go

@@ -11,6 +11,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/gorilla/handlers"
 	"github.com/gorilla/mux"
 	jose "gopkg.in/square/go-jose.v2"
 
@@ -101,7 +102,7 @@ type discovery struct {
 	Claims        []string `json:"claims_supported"`
 }
 
-func (s *Server) discoveryHandler() (http.HandlerFunc, error) {
+func (s *Server) discoveryHandler() (http.Handler, error) {
 	d := discovery{
 		Issuer:      s.issuerURL.String(),
 		Auth:        s.absURL("/auth"),
@@ -127,11 +128,18 @@ func (s *Server) discoveryHandler() (http.HandlerFunc, error) {
 		return nil, fmt.Errorf("failed to marshal discovery data: %v", err)
 	}
 
-	return func(w http.ResponseWriter, r *http.Request) {
+	var discoveryHandler http.Handler
+	discoveryHandler = http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Content-Type", "application/json")
 		w.Header().Set("Content-Length", strconv.Itoa(len(data)))
 		w.Write(data)
-	}, nil
+	})
+	if len(s.discoveryAllowedOrigins) > 0 {
+		corsOption := handlers.AllowedOrigins(s.discoveryAllowedOrigins)
+		discoveryHandler = handlers.CORS(corsOption)(discoveryHandler)
+	}
+
+	return discoveryHandler, nil
 }
 
 // handleAuthorization handles the OAuth2 auth endpoint.

server/handlers_test.go

@@ -22,3 +22,61 @@ func TestHandleHealth(t *testing.T) {
 	}
 
 }
+
+var discoveryHandlerCORSTests = []struct {
+	DiscoveryAllowedOrigins []string
+	Origin                  string
+	ResponseAllowOrigin     string //The expected response: same as Origin in case of valid CORS flow
+}{
+	{nil, "http://foo.example", ""}, //Default behavior: cross origin requests not allowed
+	{[]string{}, "http://foo.example", ""},
+	{[]string{"http://foo.example"}, "http://foo.example", "http://foo.example"},
+	{[]string{"http://bar.example", "http://foo.example"}, "http://foo.example", "http://foo.example"},
+	{[]string{"*"}, "http://foo.example", "http://foo.example"},
+	{[]string{"http://bar.example"}, "http://foo.example", ""},
+}
+
+func TestDiscoveryHandlerCORS(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	for _, testcase := range discoveryHandlerCORSTests {
+
+		httpServer, server := newTestServer(ctx, t, func(c *Config) {
+			c.DiscoveryAllowedOrigins = testcase.DiscoveryAllowedOrigins
+		})
+		defer httpServer.Close()
+
+		discoveryHandler, err := server.discoveryHandler()
+		if err != nil {
+			t.Fatalf("failed to get discovery handler: %v", err)
+		}
+
+		//Perform preflight request
+		rrPreflight := httptest.NewRecorder()
+		reqPreflight := httptest.NewRequest("OPTIONS", "/.well-kown/openid-configuration", nil)
+		reqPreflight.Header.Set("Origin", testcase.Origin)
+		reqPreflight.Header.Set("Access-Control-Request-Method", "GET")
+		discoveryHandler.ServeHTTP(rrPreflight, reqPreflight)
+		if rrPreflight.Code != http.StatusOK {
+			t.Errorf("expected 200 got %d", rrPreflight.Code)
+		}
+		headerAccessControlPreflight := rrPreflight.HeaderMap.Get("Access-Control-Allow-Origin")
+		if headerAccessControlPreflight != testcase.ResponseAllowOrigin {
+			t.Errorf("expected '%s' got '%s'", testcase.ResponseAllowOrigin, headerAccessControlPreflight)
+		}
+
+		//Perform request
+		rr := httptest.NewRecorder()
+		req := httptest.NewRequest("GET", "/.well-kown/openid-configuration", nil)
+		req.Header.Set("Origin", testcase.Origin)
+		discoveryHandler.ServeHTTP(rr, req)
+		if rr.Code != http.StatusOK {
+			t.Errorf("expected 200 got %d", rr.Code)
+		}
+		headerAccessControl := rr.HeaderMap.Get("Access-Control-Allow-Origin")
+		if headerAccessControl != testcase.ResponseAllowOrigin {
+			t.Errorf("expected '%s' got '%s'", testcase.ResponseAllowOrigin, headerAccessControl)
+		}
+	}
+}

server/server.go

@@ -42,6 +42,11 @@ type Config struct {
 	// flow. If no response types are supplied this value defaults to "code".
 	SupportedResponseTypes []string
 
+	// List of allowed origins for CORS requests on discovery endpoint.
+	// If none are indicated, CORS requests are disabled. Passing in "*" will allow any
+	// domain.
+	DiscoveryAllowedOrigins []string
+
 	// If enabled, the server won't prompt the user to approve authorization requests.
 	// Logging in implies approval.
 	SkipApprovalScreen bool
@@ -111,6 +116,8 @@ type Server struct {
 
 	supportedResponseTypes map[string]bool
 
+	discoveryAllowedOrigins []string
+
 	now func() time.Time
 
 	idTokensValidFor time.Duration
@@ -182,6 +189,7 @@ func newServer(ctx context.Context, c Config, rotationStrategy rotationStrategy)
 		connectors:              make(map[string]Connector),
 		storage:                 newKeyCacher(c.Storage, now),
 		supportedResponseTypes:  supported,
+		discoveryAllowedOrigins: c.DiscoveryAllowedOrigins,
 		idTokensValidFor:        value(c.IDTokensValidFor, 24*time.Hour),
 		skipApproval:            c.SkipApprovalScreen,
 		now:                     now,
@@ -197,6 +205,9 @@ func newServer(ctx context.Context, c Config, rotationStrategy rotationStrategy)
 	handleFunc := func(p string, h http.HandlerFunc) {
 		r.HandleFunc(path.Join(issuerURL.Path, p), h)
 	}
+	handle := func(p string, h http.Handler) {
+		r.Handle(path.Join(issuerURL.Path, p), h)
+	}
 	handlePrefix := func(p string, h http.Handler) {
 		prefix := path.Join(issuerURL.Path, p)
 		r.PathPrefix(prefix).Handler(http.StripPrefix(prefix, h))
@@ -207,7 +218,7 @@ func newServer(ctx context.Context, c Config, rotationStrategy rotationStrategy)
 	if err != nil {
 		return nil, err
 	}
-	handleFunc("/.well-known/openid-configuration", discoveryHandler)
+	handle("/.well-known/openid-configuration", discoveryHandler)
 
 	// TODO(ericchiang): rate limit certain paths based on IP.
 	handleFunc("/token", s.handleToken)