code: def _from_jwt(cls, headers, payload, key=None):
          
          jwt = Jwt(
              secret_key=key,
              issuer=payload.get('iss', None),
              subject=payload.get('sub', None),
              algorithm=headers.get('alg', None),
              valid_until=payload.get('exp', None),
              nbf=payload.get('nbf', None),
          )
          jwt.__decoded_payload = payload
          jwt.__decoded_headers = headers
          return jwt
docs: Class specific implementation of from_jwt which should take jwt components and return
          and instance of this Class with jwt information loaded.
          :return: Jwt object containing the headers, payload and key