Function sign_v4 

fn sign_v4(input: &SigV4Input<'_>) -> SigV4Output

Computes an AWS Signature Version 4 for the given request.

Pure function: given identical inputs it always produces the same output. The four SigV4 steps are: build the canonical request, form the string-to-sign, derive the signing key via the HMAC date/region/service chain, and HMAC the string-to-sign.