'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):

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