Function aws_request_signature 

pub fn aws_request_signature(
    secret: &str,
    date: &str,
    region: &str,
    service: &str,
    message: &[u8],
) -> [u8; 32]

AWS Signature Version 4 over a request’s string to sign. The signing key derives from the secret through the date, region and service scope; intermediate keys and the prefixed secret are erased on drop.