Support different signers for non AWS S3-Storage

[sstamm]

We use S3 provided by NetApp which does not support payload-signing.
To use the AWS S3Client you have to configure the Signer like:

        this.client = S3Client.builder()
            .overrideConfiguration(ClientOverrideConfiguration.builder().putAdvancedOption(SdkAdvancedClientOption.SIGNER, AwsS3V4Signer.create()).build()).build();

This change introduces s3.spi.client.custom-signer to define a customer signer class like:

    public static class Signer extends AbstractAwsS3V4Signer    {
        public Signer()        {
            //  Auto-generated constructor stub
        }
    }
...

        System.setProperty("s3.spi.client.custom-signer", Signer.class.getName());

[markjschreiber]

Thanks for suggesting this change. While reviewing I noticed that the Signer class is deprecated and the recommendation is to use the software.amazon.awssdk.http.auth.spi.signer package, which is itself an SPI and might allow you to introduce a custom signer without needing to change this package?
Can you explore this possibility? Unfortunate there doesn't seem to be much documentation on this SPI. https://sdk.amazonaws.com/java/api/latest/software/amazon/awssdk/http/auth/spi/signer/package-summary.html

[sstamm]

I am struggling at this deprication for some time because it's not clear (for me as an S3 newbie) how to adopt it.
I found: aws/aws-sdk-java-v2#5962
Any idea where I can get more information?