Group restriction bypass via bearer token in user_oidc (SETTING_RESTRICT_LOGIN_TO_GROUPS not enforced in Backend::getCurrentUserId)

Bug reported by msat was disclosed at May 21, 2026, 10:12 pm   |   Improper Access Control - Generic

A security inconsistency was identified in the user_oidc app where group-based login restrictions were enforced in the browser OIDC flow but not in bearer token validation. This could have allowed users outside whitelisted groups to access the Nextcloud API with a valid bearer token.