anchor.diff:              A comprehensive list of possible errors:
               - `AUTH_MISSING_USERNAME` if no input for `username` was submitted
               - `AUTH_MISSING_PASSWORD` if no input for `password` was submitted
  -            - `REQUEST_UNSUPPORTED_CONTENT_TYPE` if the submitted content and/or Content-Type is not `application/json`
  +            - `REQUEST_MALFORMED_DATA` if the submitted data in the request body does not match the Content-Type or is unparseable
   
   + Response 401 (application/json)
       + Attributes (object)
  
positive.code: 
              A comprehensive list of possible errors:
              - `NEED_AUTHENTICATION` if no valid session token has been supplied or the user for whom the token has been created does not exist (anymore)
  
  + Response 422 (application/json)
      + Attributes (object)
  
negative.code:             - `USER_CREATE_INVALID_USERNAME` if the supplied `username` does not match the given criteria (regex: ^[a-zA-Z0-9\-\.]{3,20}$)
              - `USER_CREATE_INVALID_PASSWORD` if the supplied `password` does not satisfy the given criteria (regex: ^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)[a-zA-Z\d]{8,}$)
              - `USER_CREATE_INVALID_EMAIL` if the supplied `email` is not a valid email
              - `REQUEST_MALFORMED_DATA` if the submitted data in the request body does not match the Content-Type or is unparseable
  
  + Response 406 (application/json)
      + Attributes (object)
          + status (string) - Textual description of the HTTP status
          + message (string) - Detailed error information, e.g. hint about malformed request
          + i18n (string) - A unique token representing above error description message; can be used for internationalization in frontends
  
              A comprehensive list of possible errors:
              - `REQUEST_UNSUPPORTED_CONTENT_TYPE` if the submitted Content-Type is not `application/json`
  
  + Response 422 (application/json)
      + Attributes (object)
  