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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _retrieve_and_validate_certificate_chain(self, cert_url):
 # type: (str) -> Certificate """Retrieve and validate certificate chain. This method validates if the URL is valid and loads and validates the certificate chain, before returning it. :param cert_url: URL for retrieving certificate chain :type cert_url: str :return The certificate chain loaded from the URL :rtype cryptography.x509.Certificate :raises: :py:class:`VerificationException` if the URL is invalid, if the loaded certificate chain is invalid """

        self._validate_certificate_url(cert_url)

        cert_chain = self._load_cert_chain(cert_url)
        self._validate_cert_chain(cert_chain)
        return cert_chain