3.12.5.1.5.2 Response Body
The response body MUST be a Proxy Token Wrapper complex type (section 2.2.2.20) if processing was successful. If processing was not successful and the status code is 400, 401, 500, or 501, the response body can be an Error Response complex type (section 2.2.2.22), but this is not required. The response body MUST be empty in all other cases.