Returns errors on:
        Certificate, PrivateKey or Chain not being properly formatted
        Arn not existing if its provided
        PrivateKey size > 2048
        Certificate expired or is not yet in effect

        Does not return errors on:
        Checking Certificate is legit, or a selfsigned chain is provided

        :return: str(JSON) for response

def import_certificate(self):
        """
        Returns errors on:
        Certificate, PrivateKey or Chain not being properly formatted
        Arn not existing if its provided
        PrivateKey size > 2048
        Certificate expired or is not yet in effect

        Does not return errors on:
        Checking Certificate is legit, or a selfsigned chain is provided

        :return: str(JSON) for response
        """
        certificate = self._get_param('Certificate')
        private_key = self._get_param('PrivateKey')
        chain = self._get_param('CertificateChain')  # Optional
        current_arn = self._get_param('CertificateArn')  # Optional

        # Simple parameter decoding. Rather do it here as its a data transport decision not part of the
        # actual data
        try:
            certificate = base64.standard_b64decode(certificate)
        except Exception:
            return AWSValidationException('The certificate is not PEM-encoded or is not valid.').response()
        try:
            private_key = base64.standard_b64decode(private_key)
        except Exception:
            return AWSValidationException('The private key is not PEM-encoded or is not valid.').response()
        if chain is not None:
            try:
                chain = base64.standard_b64decode(chain)
            except Exception:
                return AWSValidationException('The certificate chain is not PEM-encoded or is not valid.').response()

        try:
            arn = self.acm_backend.import_cert(certificate, private_key, chain=chain, arn=current_arn)
        except AWSError as err:
            return err.response()

        return json.dumps({'CertificateArn': arn})