code: def add_proof(self, certificate_metadata, merkle_proof):
          
          certificate_json = self._get_certificate_to_issue(certificate_metadata)
          certificate_json['signature'] = merkle_proof
  
          with open(certificate_metadata.blockchain_cert_file_name, 'w') as out_file:
              out_file.write(json.dumps(certificate_json))
docs: :param certificate_metadata:
          :param merkle_proof:
          :return: