Putting objects in S3 from Java application complains about missing AWS Signature

The error message indicates that you need to use AWS Signature Version 4 to authenticate your requests to Amazon S3 with Object Lock parameters. This is because Object Lock is a feature that provides WORM (Write Once Read Many) functionality, and as such, requires a higher level of security.

You can enable Signature Version 4 by removing the .withClientConfiguration(new ClientConfiguration().withSignerOverride("AWSS3V4SignerType")) line from your code. The AWS SDK for Java will automatically use Signature Version 4 if it's required for the API you're calling.

Here's an updated version of your code:

final AwsClientBuilder.EndpointConfiguration endpoint = new AwsClientBuilder.EndpointConfiguration(
            s3Endpoint,
            s3Region
    );

final AmazonS3 s3client = AmazonS3ClientBuilder
            .standard()
            .withEndpointConfiguration(endpoint)
            .enablePathStyleAccess()
            .build();

Note that it's recommended to use IAM roles or instance profiles to provide AWS credentials to applications running on EC2 or EKS, rather than using explicit access keys. This approach can help improve security and simplify credential management.