Elastica\Transport\AwsAuthV4::getSigningMiddleware PHP Method

    private function getSigningMiddleware()
    {
        $region = $this->getConnection()->hasParam('aws_region') ? $this->getConnection()->getParam('aws_region') : getenv('AWS_REGION');
        $signer = new SignatureV4('es', $region);
        $credProvider = $this->getCredentialProvider();
        return Middleware::mapRequest(function (RequestInterface $req) use($signer, $credProvider) {
            return $signer->signRequest($req, $credProvider()->wait());
        });
    }