Is it really proprietary? We now have a lot of S3 compatible servers, MinIO for example requires this type of signature for requests.
The AWS v4 signing method is a spec for how to do HMAC request signing. It is not limited to use only with AWS services.
You can use it to sign requests on any service, and there are many implementations. Here is an example of one I’ve used in the past: https://github.com/auroratechnologies/vangoh
Or as mentioned above: https://github.com/minio/minio/blob/master/cmd/signature-v4....