use API url :)

oauth3.core.js

@@ -1184,7 +1184,7 @@
         opts.api = api;
         opts.session = OAUTH3.hooks.session._getCached(this._providerUri);
 
-        return OAUTH3.api(this._providerUri, opts);
+        return OAUTH3.api(this._providerDirectives.api, opts);
       }
     };
     result.authenticate = result.login;