fix: Add Accept header to auth metadata request

Author: SVLaursen

src/client/auth.test.ts

@@ -887,7 +887,8 @@ describe('OAuth Authorization', () => {
             const calls = mockFetch.mock.calls;
             const [, options] = calls[0];
             expect(options.headers).toEqual({
-                'MCP-Protocol-Version': '2025-01-01'
+                'MCP-Protocol-Version': '2025-01-01',
+                Accept: 'application/json'
             });
         });
 

src/client/auth.ts

@@ -735,7 +735,10 @@ export async function discoverAuthorizationServerMetadata(
         protocolVersion?: string;
     } = {}
 ): Promise<AuthorizationServerMetadata | undefined> {
-    const headers = { 'MCP-Protocol-Version': protocolVersion };
+    const headers = {
+        'MCP-Protocol-Version': protocolVersion,
+        Accept: 'application/json'
+    };
 
     // Get the list of URLs to try
     const urlsToTry = buildDiscoveryUrls(authorizationServerUrl);