void sign(HttpRequest request, AuthConfig credentials, Date signingTime) {
        AwsSigner4Request sr = new AwsSigner4Request(region, service, request, signingTime);
        if(!request.containsHeader("X-Amz-Date")) {
            request.addHeader("X-Amz-Date", sr.getSigningDateTime());
        }
        request.addHeader("Authorization", task4(sr, credentials));
        final String securityToken = credentials.getAuth();
        if (StringUtils.isNotEmpty(securityToken)) {
            request.addHeader("X-Amz-Security-Token", securityToken);
        }
    }
Sign a request.  Add the headers that authenticate the request.

@param request The request to sign.
@param credentials The credentials to use when signing.
@param signingTime The invocation time to use;
src/main/java/io/fabric8/maven/docker/access/ecr/AwsSigner4.java