Make typ optional

[dajiaji]

See #641

typ value on a JWT header can be overwritten with headers argument but typ value cannot be removed. In other words, pyjwt cannot make a JWT which does not include typ.
According to RFC7519, use of the typ header parameter is OPTIONAL.

This PR keeps backward compatibility and makes kty header parameter optional like this:

token = jwt.encode({"foo", "bar"}, "mysecret", algorithm="HS256", typ="")

I'm glad if you can check and merge it.

Close #641

[auvipy]

please check the build failures

[dajiaji]

There were no practical problems, but the order of the parameters(typ, alg) in the JWT header changed, resulting in a different output from the sample code. I fixed it.

[jpadilla]

@dajiaji how about instead of adding typ as a top level kwarg, we instead allow changing it through headers?

[dajiaji]

Sorry for my late reply.

we instead allow changing it through headers?

To my understanding, we can already change "typ" through "headers", but the problem here is that you can't leave "typ" out. To solve this, you mean headers={"typ":""} is better than typ="" ?

From my point of view, since there are now several standards for typ other than JWT (e.g., dpop+jwt and scevent+jwt), it is not a bad idea to be able to change typ as a top-level argument like alg.

Anyway, if you think headers={"typ":""} is better, I can update my PR for that. No problem. Feel free to request me.

[codrinh]

Hi @jpadilla can you please provide your feedback on the previous comment. Currently this is a blocker for me, and I'm waiting for this PR to be merged into master. Thank you.

[dajiaji]

Hi, @jpadilla. I fixed it as you requested. The changes are much less. Could you check and merge it?

[dajiaji]

@jpadilla I resolved a conflict on CHANGELOG.