Hmac-dot-net-tester is a project mainly written in C#, based on the BSD-3-Clause license.
Simple HMAC HTTP Authentication tester for .NET 4.0+ (written in C#)
Simple Windows (.NET 4) app for testing HTTP HMAC authentication. Since .NET can't set the HTTP Date header, you have to use a custom header and workaround that on the server side.
Since this can make it very annoying to debug your HMAC canonical string, it's much easier to have a simple client to isolate problems.