private static byte[] getSigningKey(AwsSigner4Request sr, AuthConfig credentials) {
        byte[] kSecret = ("AWS4" + credentials.getPassword()).getBytes(StandardCharsets.UTF_8);
        byte[] kDate = hmacSha256(kSecret, sr.getSigningDate());
        byte[] kRegion = hmacSha256(kDate, sr.getRegion());
        byte[] kService = hmacSha256(kRegion, sr.getService());
        return hmacSha256(kService, "aws4_request");
    }
Task 3.
<a href="https://docs.aws.amazon.com/general/latest/gr/sigv4-create-string-to-sign.html">Calculate the Signature for AWS Signature Version 4</a>
src/main/java/io/fabric8/maven/docker/access/ecr/AwsSigner4.java