feat(auth): implement proxied /.well-known/oauth-authorization-server (#244)

Signed-off-by: Marc Nuri <marc@marcnuri.com>

pkg/http/authorization.go

@@ -22,7 +22,7 @@ const (
 func AuthorizationMiddleware(requireOAuth bool, serverURL string, oidcProvider *oidc.Provider, mcpServer *mcp.Server) func(http.Handler) http.Handler {
 	return func(next http.Handler) http.Handler {
 		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-			if r.URL.Path == healthEndpoint || r.URL.Path == oauthProtectedResourceEndpoint {
+			if r.URL.Path == healthEndpoint || r.URL.Path == oauthProtectedResourceEndpoint || r.URL.Path == oauthAuthorizationServerEndpoint {
 				next.ServeHTTP(w, r)
 				return
 			}

pkg/http/http.go

@@ -44,6 +44,7 @@ func Serve(ctx context.Context, mcpServer *mcp.Server, staticConfig *config.Stat
 	mux.HandleFunc(healthEndpoint, func(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusOK)
 	})
+	mux.HandleFunc(oauthAuthorizationServerEndpoint, OAuthAuthorizationServerHandler(staticConfig))
 	mux.HandleFunc(oauthProtectedResourceEndpoint, OAuthProtectedResourceHandler(mcpServer, staticConfig))
 
 	ctx, cancel := context.WithCancel(ctx)

pkg/http/http_test.go

@@ -286,6 +286,36 @@ func TestHealthCheck(t *testing.T) {
 	})
 }
 
+func TestWellKnownOAuthAuthorizationServer(t *testing.T) {
+	// Simple http server to mock the authorization server
+	testServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != "/.well-known/oauth-authorization-server" {
+			http.NotFound(w, r)
+			return
+		}
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write([]byte(`{"issuer": "https://example.com"}`))
+	}))
+	t.Cleanup(testServer.Close)
+	testCaseWithContext(t, &httpContext{StaticConfig: &config.StaticConfig{AuthorizationURL: testServer.URL, RequireOAuth: true}}, func(ctx *httpContext) {
+		resp, err := http.Get(fmt.Sprintf("http://%s/.well-known/oauth-authorization-server", ctx.HttpAddress))
+		t.Cleanup(func() { _ = resp.Body.Close() })
+		t.Run("Exposes .well-known/oauth-authorization-server endpoint", func(t *testing.T) {
+			if err != nil {
+				t.Fatalf("Failed to get .well-known/oauth-authorization-server endpoint: %v", err)
+			}
+			if resp.StatusCode != http.StatusOK {
+				t.Errorf("Expected HTTP 200 OK, got %d", resp.StatusCode)
+			}
+		})
+		t.Run(".well-known/oauth-authorization-server returns application/json content type", func(t *testing.T) {
+			if resp.Header.Get("Content-Type") != "application/json" {
+				t.Errorf("Expected Content-Type application/json, got %s", resp.Header.Get("Content-Type"))
+			}
+		})
+	})
+}
+
 func TestWellKnownOAuthProtectedResource(t *testing.T) {
 	testCase(t, func(ctx *httpContext) {
 		resp, err := http.Get(fmt.Sprintf("http://%s/.well-known/oauth-protected-resource", ctx.HttpAddress))

pkg/http/wellknown.go

@@ -2,6 +2,7 @@ package http
 
 import (
 	"encoding/json"
+	"io"
 	"net/http"
 
 	"github.com/containers/kubernetes-mcp-server/pkg/config"
@@ -9,9 +10,42 @@ import (
 )
 
 const (
-	oauthProtectedResourceEndpoint = "/.well-known/oauth-protected-resource"
+	oauthAuthorizationServerEndpoint = "/.well-known/oauth-authorization-server"
+	oauthProtectedResourceEndpoint   = "/.well-known/oauth-protected-resource"
 )
 
+func OAuthAuthorizationServerHandler(staticConfig *config.StaticConfig) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		if staticConfig.AuthorizationURL == "" {
+			http.Error(w, "Authorization URL is not configured", http.StatusNotFound)
+			return
+		}
+		req, err := http.NewRequest(r.Method, staticConfig.AuthorizationURL+oauthAuthorizationServerEndpoint, nil)
+		if err != nil {
+			http.Error(w, "Failed to create request: "+err.Error(), http.StatusInternalServerError)
+			return
+		}
+		resp, err := http.DefaultClient.Do(req.WithContext(r.Context()))
+		if err != nil {
+			http.Error(w, "Failed to perform request: "+err.Error(), http.StatusInternalServerError)
+			return
+		}
+		defer func() { _ = resp.Body.Close() }()
+		body, err := io.ReadAll(resp.Body)
+		if err != nil {
+			http.Error(w, "Failed to read response body: "+err.Error(), http.StatusInternalServerError)
+			return
+		}
+		for key, values := range resp.Header {
+			for _, value := range values {
+				w.Header().Add(key, value)
+			}
+		}
+		w.WriteHeader(resp.StatusCode)
+		_, _ = w.Write(body)
+	}
+}
+
 func OAuthProtectedResourceHandler(mcpServer *mcp.Server, staticConfig *config.StaticConfig) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Content-Type", "application/json")