Bypass Cognito hosted UI when federated IdP is configured

mcp/packages/server/src/moneta/cognito.ts

@@ -172,13 +172,14 @@ export class CognitoClient {
 
     private async tokenRequest(params: Record<string, string>): Promise<CognitoTokenResponse> {
         const discovery = await this.discovery();
+        const tokenEndpoint = this.config.upstreamTokenUrl ?? discovery.token_endpoint;
         const body = new URLSearchParams({ ...params, client_id: this.config.clientId });
         const headers: Record<string, string> = { "Content-Type": "application/x-www-form-urlencoded" };
         if (this.config.clientSecret) {
             const basic = Buffer.from(`${this.config.clientId}:${this.config.clientSecret}`).toString("base64");
             headers["Authorization"] = `Basic ${basic}`;
         }
-        const response = await fetch(discovery.token_endpoint, { method: "POST", headers, body });
+        const response = await fetch(tokenEndpoint, { method: "POST", headers, body });
         if (!response.ok) {
             const detail = await response.text().catch(() => "");
             throw new Error(`Cognito token endpoint returned ${response.status}: ${detail.slice(0, 300)}`);
@@ -261,14 +262,18 @@ export class CognitoClient {
     /** Builds the upstream authorize redirect with our own callback, state and PKCE pair. */
     async authorizeUrl(state: string, codeChallenge: string): Promise<string> {
         const discovery = await this.discovery();
-        const url = new URL(discovery.authorization_endpoint);
+        const baseEndpoint = this.config.upstreamAuthUrl ?? discovery.authorization_endpoint;
+        const url = new URL(baseEndpoint);
         url.searchParams.set("response_type", "code");
         url.searchParams.set("client_id", this.config.clientId);
         url.searchParams.set("redirect_uri", this.config.callbackUrl);
         url.searchParams.set("scope", UPSTREAM_SCOPE);
         url.searchParams.set("state", state);
         url.searchParams.set("code_challenge", codeChallenge);
         url.searchParams.set("code_challenge_method", "S256");
+        if (this.config.identityProvider) {
+            url.searchParams.set("identity_provider", this.config.identityProvider);
+        }
         return url.href;
     }
 }

mcp/packages/server/src/moneta/config.ts

@@ -48,6 +48,10 @@ export interface MonetaAuthConfig {
     storageUrl: string | undefined;
     /** Key material for at-rest encryption of OAuth state in Valkey. */
     encryptionSecret: string | undefined;
+    /** Override Cognito's authorization_endpoint with a custom auth proxy URL (e.g. mpass-auth-proxy). */
+    upstreamAuthUrl: string | undefined;
+    /** Override Cognito's token_endpoint with a custom auth proxy URL (e.g. mpass-auth-proxy). */
+    upstreamTokenUrl: string | undefined;
     isProduction: boolean;
 }
 
@@ -96,6 +100,9 @@ export function loadMonetaAuthConfig(): MonetaAuthConfig {
         );
     }
 
+    const upstreamAuthUrl = (process.env.COGNITO_UPSTREAM_AUTH_URL ?? "").trim() || undefined;
+    const upstreamTokenUrl = (process.env.COGNITO_UPSTREAM_TOKEN_URL ?? "").trim() || undefined;
+
     const origins = csv(process.env.MCP_ALLOWED_ORIGINS);
     const redirectUris = csv(process.env.MCP_ALLOWED_CLIENT_REDIRECT_URIS);
 
@@ -111,6 +118,8 @@ export function loadMonetaAuthConfig(): MonetaAuthConfig {
         allowedClientRedirectUris: redirectUris.length > 0 ? redirectUris : null,
         storageUrl,
         encryptionSecret,
+        upstreamAuthUrl,
+        upstreamTokenUrl,
         isProduction: (process.env.MCP_ENV ?? "production") === "production",
     };
 }