Generate test signature

[jgayfer]

Problem

Testing signature verification end to end is challenging, as it requires generating a time sensitive, encoded signature.

There are options to work around this like stubs, or alternate code flows under test, but ideally an integration test goes completely end to end, where the incoming request + signature is fully validated.

Solution

It would be great if this crate provided a way to more easily generate test signatures.

Other Stripe libraries provide this functionality, like stripe-node.

Alternatives

The signature can be generated manually, but it's an error prone operation that would be great to have a standard definition for.

I'm aware that #374 exists, but it doesn't lend itself to full end to end testing as it requires an alternative code flow.

[arlyon]

Hi! I am going to label this as a feature request. I don't currently have bandwidth to take this on at the moment but very happy to help with the PR (if someone beats me to it..).

Cheers

Alex