Presigned requests only support SigV4

[lauzadis]

Describe the bug

Presigners assume the request is always presigned with SigV4. This means alternate auth schemes (like SigV4a, SigV4S3Express) cannot be used for presigning.

Expected behavior

A presigned request should use whichever auth scheme would be used when making the normal, non-presigned request (i.e, the auth scheme resolved from endpoint rules).

Current behavior

The presigner uses SigV4

Steps to Reproduce

Make a presigned request which would normally result in SigV4a or SigV4S3Express being used. Observe that SigV4 is used instead.

Possible Solution

The relevant section is here: https://github.com/awslabs/smithy-kotlin/blob/main/runtime/auth/aws-signing-common/common/src/aws/smithy/kotlin/runtime/auth/awssigning/Presigner.kt#L37

It will likely require another overhaul of the presigner, since the last refactor was done before the auth refactor.

Context

No response

AWS Kotlin SDK version used

1.0.66

Platform (JVM/JS/Native)

JVM

Operating System and version

macOS Sonoma