feat(auth): add support for openidconnect

[Bnyro]

Test setup:

docker run -p 9400:9400 ghcr.io/geigerzaehler/oidc-provider-mock

Then, start the sync-server with cargo run.

Actual testing:

• Visit http://localhost:8080/v1/account/oidc/authenticate?redirect_url=https://example.com, insert some random user name and continue.
• Observe that there's now an auth token param in the URL you got redirected to
• Visit http://localhost:8080/v1/account/oidc/delete?redirect_url=https://example.com
• Observe that the account gets deleted if it exists (and otherwise you get an error)

Information about OIDC if you're not familiar with the protocol: https://spapas.github.io/2023/11/29/openid-connect-tutorial/

[Bnyro]

cc @sourcenix, would be great if you could review it when you have time

[sourcenix]

thread 'tokio-rt-worker' (21957) panicked at src/main.rs:122:53:
called `Result::unwrap()` on an `Err` value: QueryError(DieselMigrationName { name: "2026-07-26-080240-0000_add-oidc", version: MigrationVersion("202607260802400000") }, DatabaseError(Unknown, "Cannot add a UNIQUE column"))
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

thread 'main' (16866) panicked at src/main.rs:126:10:
called `Result::unwrap()` on an `Err` value: DatabaseError(UnableToSendCommand, "task 7 panicked with message \"called `Result::unwrap()` on an `Err` value: QueryError(DieselMigrationName { name: \\\"2026-07-26-080240-0000_add-oidc\\\", version: MigrationVersion(\\\"202607260802400000\\\") }, DatabaseError(Unknown, \\\"Cannot add a UNIQUE column\\\"))\"")

Diesel retrieves an error while initializing the database.

[Bnyro]

thread 'tokio-rt-worker' (21957) panicked at src/main.rs:122:53:
called `Result::unwrap()` on an `Err` value: QueryError(DieselMigrationName { name: "2026-07-26-080240-0000_add-oidc", version: MigrationVersion("202607260802400000") }, DatabaseError(Unknown, "Cannot add a UNIQUE column"))
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

thread 'main' (16866) panicked at src/main.rs:126:10:
called `Result::unwrap()` on an `Err` value: DatabaseError(UnableToSendCommand, "task 7 panicked with message \"called `Result::unwrap()` on an `Err` value: QueryError(DieselMigrationName { name: \\\"2026-07-26-080240-0000_add-oidc\\\", version: MigrationVersion(\\\"202607260802400000\\\") }, DatabaseError(Unknown, \\\"Cannot add a UNIQUE column\\\"))\"")

Diesel retrieves an error while initializing the database.

Oh, sorry for that. I added the UNIQUE constraint after testing everything and didn't re-run the migrations, I thought it would work like that...

For testing it's sufficient to just remove the UNIQUE consteaint for now.

[sourcenix]

LGTM

[Bnyro]

Thanks for the reviews everyone 👍