code: async def add_claims(self, payload, user, *args, **kwargs):
          
          delta = timedelta(seconds=self.config.expiration_delta())
          exp = datetime.utcnow() + delta
          additional = {"exp": exp}
  
          for option in ["iss", "iat", "nbf", "aud"]:
              setting = "claim_{}".format(option.lower())
              if setting in self.config:  # noqa
                  attr = self.config.get(setting)
                  if attr:
                      self.claims.append(option)
                      method_name = "build_claim_{}".format(option)
                      method = getattr(utils, method_name)
                      additional.update({option: method(attr, self.config)})
  
          payload.update(additional)
  
          if self._custom_claims:
              custom_claims = {}
              for claim in self._custom_claims:
                  custom_claims[claim.get_key()] = await utils.call(
                      claim.setup, payload, user
                  )
              payload.update(custom_claims)
  
          return payload
docs: Injects standard claims into the payload for: exp, iss, iat, nbf, aud.
          And, custom claims, if they exist