code: async def encode_jwt(self, identity: SessionIdentity) -> str:
          
      
          assert identity
  
          payload = {
              "sub": identity.identity,
              "user_id": identity.user_id,
              "exp": int(time.time() + self._max_age) # seconds from 1970-1-1 UTC
          }
          
          if identity.client_id:
              payload['aud'] = identity.client_id
  
  
          token = jwt.encode({'alg': 'HS256'}, payload, self._secure_key)
  
          return token.decode('ascii')
docs: 将identity编码为JWT