support decoding and encoding DEFLATE-encoded JWT bodies

[Roguelazer]

These are used in the Smart Health Card framework that several regions (including California and Quebec) are using for COVID-19 proofs of vaccination, and are supported by some other JWT libraries, such as jwt-go.

If y'all like this approach, I'm glad to write tests. I could also see putting this logic in api_jws.py.

[tahnok]

I'd also volunteer to help write some tests. I am also looking at decoding the data in an SHC encoded JWT and at the moment pyjwt cannot be used for this

Overall, change looks solid and straightforward

[auvipy]

I think we can add this

[auvipy]

I'd also volunteer to help write some tests. I am also looking at decoding the data in an SHC encoded JWT and at the moment pyjwt cannot be used for this

Overall, change looks solid and straightforward

you are welcome to do so

[tahnok]

I added some tests in this commit tahnok@5d15874 if you want to pull it into your branch @Roguelazer

[akx]

Hmm – I'd be a little wary against adding a non-spec feature like this. In fact, the golang library PR @Roguelazer merged was actually not merged due to the same concern: dgrijalva/jwt-go#102 (comment)

I think the better approach would be to refactor payload decoding (lines 98..104 in the preimage) to a separate function that can be easily augmented in a subclass.

[jpadilla]

Closing this one for now, same reason as #753.