Enable support for FIPS endpoints

[wbrown64]

I have a requirement to use FIPS endpoints for accessing S3 buckets as described here https://aws.amazon.com/compliance/fips/#FIPS_Endpoints_by_Service. However based on docs, I can either a) not see a way to enable this endpoint usage, or b) verify that the parameter AWS_S3_ENDPOINT has any effect on the endpoint used, and overall not verify that a FIPS endpoint is being used. I was wondering if this functionality already existed, and/or if it could be built in. Thanks in advance.