code: def authorization_header_parameters(self):
          
          result = getattr(self, "_authorization_header_parameters", None)
          if result is None:
              auth = self.headers.get(_authorization)
              if auth is None:
                  raise AttributeError("Authorization header is not present")
              
              if not auth.startswith(AWS4_HMAC_SHA256 + " "):
                  raise AttributeError("Authorization header is not AWS SigV4")
  
              result = {}
              for parameter in auth[len(AWS4_HMAC_SHA256)+1:].split(","):
                  parameter = parameter.strip()
                  try:
                      key, value = parameter.split("=", 1)
                  except ValueError:
                      raise AttributeError(
                          "Invalid Authorization header: missing '='")
  
                  if key in result:
                      raise AttributeError(
                          "Invalid Authorization header: duplicate key %r" % key)
                  
                  result[key] = value
              
              self._authorization_header_parameters = result
          return result
docs: The parameters from the Authorization header (only).  If the
          Authorization header is not present or is not an AWS SigV4 header, an
          AttributeError exception is raised.