code: def get_access_token(self, http=None, additional_claims=None):
          
          if additional_claims is None:
              if self.access_token is None or self.access_token_expired:
                  self.refresh(None)
              return client.AccessTokenInfo(
                access_token=self.access_token, expires_in=self._expires_in())
          else:
              # Create a 1 time token
              token, unused_expiry = self._create_token(additional_claims)
              return client.AccessTokenInfo(
                access_token=token, expires_in=self._MAX_TOKEN_LIFETIME_SECS)
docs: Create a signed jwt.
  
          Args:
              http: unused
              additional_claims: dict, additional claims to add to
                  the payload of the JWT.
          Returns:
              An AccessTokenInfo with the signed jwt