Delete a signing certificate associated with a user.

        If the user_name is not specified, it is determined implicitly based
        on the AWS Access Key ID used to sign the request.

        :type user_name: string
        :param user_name: The username of the user

        :type cert_id: string
        :param cert_id: The ID of the certificate.

def delete_signing_cert(self, cert_id, user_name=None):
        """
        Delete a signing certificate associated with a user.

        If the user_name is not specified, it is determined implicitly based
        on the AWS Access Key ID used to sign the request.

        :type user_name: string
        :param user_name: The username of the user

        :type cert_id: string
        :param cert_id: The ID of the certificate.

        """
        params = {'CertificateId' : cert_id}
        if user_name:
            params['UserName'] = user_name
        return self.get_response('DeleteSigningCertificate', params)