<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def sign(self):
 """Generates a signature"""

        payload = self._payload()
        sigin = b'.'.join([self.protected.encode('utf-8'), payload])
        signature = self.engine.sign(self.key, sigin)
        return {'protected': self.protected,
                'payload': payload,
                'signature': base64url_encode(signature)}