Cannot create CloudFront signed urls (hardcodes no longer supported RSA-SHA1, no option to use secure RSA-SHA256)

[xnox]

Describe the bug

Cannot create CloudFront signed urls with RSA key use SHA1 based signatures.

These are deprecated and removed from all hardened implementations (non-fips / ietf) but also deprecated and removed from FIPS implementations (for example AmazonLinux 2023 FIPS with OpenSSL)

Regression Issue

• Select this option if this issue appears to be a regression.

Expected Behavior

RSA signatures use SHA256

Current Behavior

RSA signatures hard-code SHA1

Reproduction Steps

Put AmazonLinux 2023 into FIPS mode
Install aws-sdk-net
Attempt to create RSA signed S3 URL

Possible Solution

Upgrade to SHA256 RSA signatures

Additional Information/Context

No response

AWS .NET SDK and/or Package version used

All

Targeted .NET Platform

All

Operating System and version

All Linux in FIPS mode

[dscpinheiro]

We'll bring this up with the CloudFront team, we're already discussing some potential signer improvements with them for #4304

[xnox]

We'll bring this up with the CloudFront team, we're already discussing some potential signer improvements with them for #4304

Adding ECDSA P-256 with SHA256 would be an easy non-breaking change win; if all the SDKs did not yet use ECDSA at all.