def METHOD_NAME(self) -> str:
    params = json.loads(self.body)
    certificate_authority_arn = params.get("CertificateAuthorityArn")
    certificate_arn = params.get("CertificateArn")
    certificate, certificate_chain = self.acmpca_backend.METHOD_NAME(
        certificate_authority_arn=certificate_authority_arn,
        certificate_arn=certificate_arn,
    )
    return json.dumps(
        dict(
            Certificate=certificate.decode("utf-8"),
            CertificateChain=certificate_chain,
        )
    )