docs: def get_tokens(self, auth, username=None):
          """
          Returns the tokens owned by the specified user. If no user is specified,
          uses the user authenticated by ``auth``.
  
          :param auth.Authentication auth: authentication for user to retrieve.
                                           Must be a username-password authentication,
                                           due to a restriction of the Gogs API
          :param str username: username of owner of tokens
  
          :return: list of tokens
          :rtype: List[Token]
          :raises NetworkFailure: if there is an error communicating with the server
          :raises ApiFailure: if the request cannot be serviced
          """
          if username is None:
              username = self.authenticated_user(auth).username
          response = self.get("/users/{u}/tokens".format(u=username), auth=auth)
          return [Token.from_json(o) for o in response.json()]