Add serialization support for DPoP tokens

[snarfed]

• requests_oauth2client version: head
• Python version: 3.12.8
• Operating System: macOS

Description

Hi again! I tried to use BearerTokenSerializer to serialize a DPoPToken, and it seemed to serialize ok, but deserializing raised UnsupportedTokenType: Unsupported token_type: DPoP:

requests_oauth2client/requests_oauth2client/tokens.py

Lines 297 to 298 in 56b93c9

	if token_type.title() != self.TOKEN_TYPE.title():
	raise UnsupportedTokenType(token_type)

So, looks like we need a DPoPTokenSerializer? Happy to whip up a PR for that, should hopefully be a pretty minimal subclass of BearerTokenSerializer.

[snarfed]

@guillp I have a PR for this in snarfed#1 that's working for me. Right now I've based it on #119's branch, so ideally we'd merge that first, but I don't know that the two PRs are directly dependent, so I can untangle that if you want.

[guillp]

Thanks for your efforts and PR. I'm going on holidays far away from the computer for 2 weeks. Hopefully I'll have a look at your PR(s) when I'll be back.
Cheers

[guillp]

closing after release of v1.7.0

[snarfed]

@guillp I'm just getting back to this now. Did v1.7.0 add serialization support for DPoP tokens? I'm not seeing it in either the code or docs, but maybe I'm missing it...?

I still need it, so I'm happy to rebase snarfed#1 onto current head if you're open to it.

[snarfed]

I went ahead and updated the PR and reopened it here, #174