Lock goth/gothic and Re-attempt OAuth2 registration on login if registration failed at startup

[zeripath]

This PR has two parts:

• Add locking to goth and gothic calls with a RWMutex

The goth and gothic calls are currently unlocked and thus are a cause of multiple potential races

• Reattempt OAuth2 registration on login if registration failed

If OAuth2 registration fails at startup we currently disable the login_source however an alternative approach could be to reattempt registration on login attempt.

Fix #16096

[zeripath]

backporting the locking to 1.15 is quite easy and given #14116 we're should be ok to backport completely. but... backporting the re-attempt registration will involve changing the signature of oauth2.Auth to add in all of the arguments necessary to call RegisterProvider.

[lunny]

These codes added here to allow Gitea start up when some auth sources take down temporarily.

[zeripath]

Yes.

The proposed changes in the Auth and Callback handlers allow us to stop auto disabling and reattempt to register at login time if registration failed at startup.

(But you've reminded me I need to recheck GetProviders once we have the hard lock to prevent double registration.)

If that "second" attempt at registration fails again then the user will be presented with a 500 page - but it genuinely is an internal server error at that point - although I fully expect that there will be complaints about that too.

(Hopefully such complaints would actually come with logs so we could at least attempt to present a nicer error page.)

[zeripath]

(But you've reminded me I need to recheck GetProviders once we have the hard lock to prevent double registration.)

Actually we're ok from the double register PoV but the issue is that RegisterSource could be somewhat slow so users may double/triple attempt to login. Will have a think.

[zeripath]

Hmm... looking at routers/web/user/auth.go:582 and the changes made by #14116 resetting is actually already handled.

So I'll let #14116 handle the re-registration attempt.

[codecov-commenter]

Codecov Report

Merging #16564 (da50ede) into main (5b2e2d2) will increase coverage by 0.00%.
The diff coverage is 15.38%.

@@           Coverage Diff           @@
##             main   #16564   +/-   ##
=======================================
  Coverage   45.41%   45.42%           
=======================================
  Files         749      749           
  Lines       84457    84465    +8     
=======================================
+ Hits        38353    38365   +12     
+ Misses      39928    39923    -5     
- Partials     6176     6177    +1     

Impacted Files	Coverage Δ
services/auth/source/oauth2/providers.go	5.17% <0.00%> (-0.29%)	⬇️
services/auth/source/oauth2/source_callout.go	0.00% <0.00%> (ø)
services/auth/source/oauth2/init.go	35.71% <66.66%> (+9.04%)	⬆️
modules/queue/unique_queue_disk_channel.go	47.26% <0.00%> (-1.37%)	⬇️
services/pull/pull.go	41.81% <0.00%> (ø)
modules/git/blame.go	67.14% <0.00%> (+1.42%)	⬆️
modules/log/file.go	75.20% <0.00%> (+1.60%)	⬆️
modules/notification/mail/mail.go	38.23% <0.00%> (+1.96%)	⬆️
modules/process/manager.go	75.30% <0.00%> (+2.46%)	⬆️
services/mailer/mail_comment.go	85.18% <0.00%> (+7.40%)	⬆️
... and 1 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 5b2e2d2...da50ede. Read the comment docs.

[zeripath]

make lgtm work