code: def private_key(self, private_key):
          
          if private_key is None:
              raise ValueError("Invalid value for `private_key`, must not be `None`")
          if private_key is not None and len(private_key) > 3000:
              raise ValueError("Invalid value for `private_key`, length must be less than or equal to `3000`")
  
          self._private_key = private_key
docs: Sets the private_key of this GlobalSignCredentials.
          The private key that matches the client certificate to allow HTTPS connection over TLS/SSL. The private key may be encrypted using a symmetric encryption key derived from a passphrase. The private key must be in PEM format. 
  
          :param private_key: The private_key of this GlobalSignCredentials.
          :type: str