refactor(auth-qrcode): Use oauth2 crate instead of openidconnect

[zecakeh]

The "next-gen auth" MSCs are now only based on OAuth 2.0, which is simpler than OpenID Connect.

This sholdn't break anything but I haven't tested it in production.

[codecov]

Codecov Report

Attention: Patch coverage is 95.45455% with 2 lines in your changes missing coverage. Please review.

Project coverage is 85.72%. Comparing base (57919f5) to head (049021f).
Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
...ates/matrix-sdk/src/authentication/qrcode/login.rs	84.61%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4604      +/-   ##
==========================================
- Coverage   85.73%   85.72%   -0.01%     
==========================================
  Files         291      291              
  Lines       33288    33282       -6     
==========================================
- Hits        28538    28531       -7     
- Misses       4750     4751       +1     

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[bnjbvr]

Is there some context to this change, some Github issue with a rationale maybe?

[zecakeh]

There is a bit of rationale in #4593 and #4550.

One of the main differences between OAuth 2.0 and OIDC is that the latter requires the use of an id_token, which is something that is NOT in OAuth 2.0. So the openidconnect crate will require fields related to it in responses from the server, but it is not something that is mandated anymore by the MSCs.

[bnjbvr]

I skimmed the changes and they seem pretty simple, thanks a bunch. In terms of requirements before landing, I'd like to make sure this is tested in some of the EX apps before we merge this.

[bnjbvr]

2025

[bnjbvr]

can this be type OauthClientInner = BasicClient<EndpointNotSet, ...> to avoid the generics? And if OauthClientInner is used only a single time, we can even inline the type declaration into its one use, likely?

[zecakeh]

Indeed, let's inline this, I was hesitating whether to do it or not.

[zecakeh]

FWIW, I tested this via the qr-login example with beta.matrix.org and it works.