3.1.5.1.1 Processing a Malformed Request
If the request does not adhere to schema rules, the request is malformed and MUST be rejected with a reasonPhrase set to "Request Malformed". If the request adheres to schema rules, except that the number of credentialsRequest in the XML request is greater than the maxOccurs attribute in the schema, the request is not considered malformed. In this case, the reasonPhrase in the error response MUST be "Request Too Large".