code: def _make_signature(self, header_b64, payload_b64, signing_key):
          
          token_segments = [header_b64, payload_b64]
          signing_input = b'.'.join(token_segments)
  
          signer = self._get_signer(signing_key)
          signer.update(signing_input)
          signature = signer.finalize()
  
          raw_signature = der_to_raw_signature(signature, signing_key.curve)
          return base64url_encode(raw_signature)
docs: Sign a serialized header and payload.
          Return the urlsafe-base64-encoded signature.