Update oauth2 and remove failure dependency

[Turbo87]

This PR updates the oauth2 dependency to the latest v4 pre-release (see ramosbugs/oauth2-rs#99). This allows us to finally get rid of the failure dependency, because oauth2 v3 was our last dependency using it.

r? @jtgeibel

[pietroalbini]

r? @pietroalbini

I'm slightly worried about upgrading to a pre-release for a library related to authentication. Is there a reason for this other than just removing failure?

[Turbo87]

I'm slightly worried about upgrading to a pre-release for a library related to authentication. Is there a reason for this other than just removing failure?

nope, that was my only reason. and I generally share your concern about the pre-release version. I looked at ramosbugs/oauth2-rs#99 and saw that the list of v4 was almost done though, and since the update was building fine and the test suite passing I was somewhat confident in this. we can also move this to WIP status though and wait for their final release.

[pietroalbini]

Yeah let's wait until the final release.

[bors]

☔ The latest upstream changes (presumably #2989) made this pull request unmergeable. Please resolve the merge conflicts.

Note that reviewers usually do not review pull requests until merge conflicts are resolved! Once you resolve the conflicts, you should change the labels applied by bors to indicate that your PR is ready for review. Post this as a comment to change the labels:

@rustbot modify labels: +S-waiting-on-review -S-waiting-on-author

[Turbo87]

closing for now until a stable oauth2 release exists