presto-elasticsearch/src/main/java/io/prestosql/elasticsearch/client/AwsRequestSigner.java/AwsRequestSigner/AwsRequestSigner
class AwsRequestSigner:    public AwsRequestSigner(String region, AWSCredentialsProvider credentialsProvider)
    {
        this.credentialsProvider = credentialsProvider;
        this.signer = new AWS4Signer();

        signer.setServiceName(SERVICE_NAME);
        signer.setRegionName(region);
    }