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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 _use_private_key( self, client_certchain_file: str, client_key_file: str, client_key_type: OpenSslFileTypeEnum, client_key_password: str ) -> None: """The certificate chain file must be in PEM format. Private method because it should be set via the constructor. """

        # Ensure the files exist
        with open(client_certchain_file):
            pass
        with open(client_key_file):
            pass

        self._ssl_ctx.use_certificate_chain_file(client_certchain_file)
        self._ssl_ctx.set_private_key_password(client_key_password)
        try:
            self._ssl_ctx.use_PrivateKey_file(client_key_file, client_key_type.value)
        except OpenSSLError as e:
            if 'bad password read' in str(e) or 'bad decrypt' in str(e):
                raise ValueError('Invalid Private Key')
            else:
                raise

        self._ssl_ctx.check_private_key()