chore: upgrade to jose v4 library

[mitar]

Related Issue or Design Document

Fixes #797.

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Further comments

This is just a formality upgrade to v4 of the library, but it does not really take advantage of the new features v4 support. For that I think we should have a more thorough rewrite of current codebase related to JWTs. I was looking into that but it is really hard to do it unless we have clear understanding that this should be done and what can we break in terms of backwards compatibility. Because there are some simple structures we have in fosite/token/jwt package which could probably just be removed and delegated to go-jose directly. I think current fosite/token/jwt was written to be backwards compatible with prior version of fosite/token/jwt which used a much smaller jwt library so a lot of logic had to be done in fosite/token/jwt. But now fosite/token/jwt is doing very strange loops where it duplicates a lot of structs and work of go-jose. For example, fosite/token/jwt validates the token using go-jose (using all reasonable algorithms) and then checks if it matches the expected signing algorithm. It would be much better if we would just give to go-jose the signing algorithm which we expect in the first place and then we do not have to do no checks anymore in fosite/token/jwt (which was the reason for v4 in the first place). Similarly with private/public keys. We do a lot of work where we take private/public keys and inspect them and reconstruct them and then pass them to go-jose. But go-jose already supports all of that and you can already pass keys directly (which is what #799 was about), even more, you can pass whole key sets directly and it picks the correct key (which fosite also tries to do). I also think fosite is probably susceptible to this attack with current approach of just blindly validating tokens and only then (sometimes) checking if signing algorithm is what was expected (I see GetRequestObjectSigningAlgorithm and GetTokenEndpointAuthSigningAlgorithm, but nothing to check when validating tokens themselves, like in introspect endpoint). Maybe I am missing something.

TLDR; I think this upgrade is the first step, but somebody with executive permissions to break backwards compatibility should give some love and cleanup current jwt codebase in fosite.

[mitar]

(CI is failing because Hydra has not been upgraded to jose v4.)