code: public Response handle(
              AuthleteApi api, TokenRequestHandlerSpi spi,
              MultivaluedMap<String, String> parameters, String authorization)
      {
          return handle(api, spi, parameters, authorization, null);
      }
docs: Handle a token request.
  
  This method is an alias of the {@link #handle(AuthleteApi,
  TokenRequestHandlerSpi, MultivaluedMap, String, String[]) handle()}
  method that accepts 5 arguments.
  
  @param api
  An implementation of {@link AuthleteApi}.
  
  @param spi
  An implementation of {@link TokenRequestHandlerSpi}.
  
  @param parameters
  Request parameters of the token request.
  
  @param authorization
  The value of {@code Authorization} header of the token request.
  
  @return
  A response that should be returned to the client application.