def validate_session(self, client, session):
        """Validate this session before use with client.

        Raises error if this session is logged in as a different user or
        the client is not the one that created the session.
        """
        if session:
            if session._client is not client:
                raise InvalidOperation(
                    'Can only use session with the MongoClient that'
                    ' started it')
            if session._authset != self.authset:
                raise InvalidOperation(
                    'Cannot use session after authenticating with different'
                    ' credentials')
Validate this session before use with client.

        Raises error if this session is logged in as a different user or
        the client is not the one that created the session.
        
stackoverflow/venv/lib/python3.6/site-packages/pymongo/pool.py