## Description In https://gitlab.com/gitlab-org/gitlab/-/issues/422952 we delivered OAuth-based authentication in the Web IDE. This feature delivered significant user benefits because it's required by high level features in the Web IDE: 1. Settings Sync support to persist user preferences across sessions. https://gitlab.com/groups/gitlab-org/-/epics/11147 2. Enabling the Language Server in the Web IDE. https://gitlab.com/groups/gitlab-org/-/epics/14203 3. Extensions Marketplace. OAuth-based authentication in the Web IDE is enabled on `gitlab.com` but the implementation is hidden behind a feature flag. Self-managed instances still rely on cookie-based authentication. The **goal** of this epic is enabled OAuth-based authentication by default on all GitLab instances. ## Acceptance criteria * [x] [**Prevent misconfigurations when admin updates the Web IDE OAuth application**](https://gitlab.com/gitlab-org/gitlab/-/issues/433322) * [x] [**Notify users when Web IDE OAuth application is configured for a different domain**](https://gitlab.com/gitlab-org/gitlab-web-ide/-/issues/287) * [x] [**Notify admins when visiting the GitLab application from a URL that doesn't match the domain specified in the GitLab instance configuration**](https://gitlab.com/gitlab-org/gitlab-web-ide/-/issues/351) * [x] [**Web IDE OAuth: Handle relative url root case**](https://gitlab.com/gitlab-org/gitlab/-/issues/475276) * [x] [**\[Feature flag\] Enable web_ide_oauth feature flag by default**](https://gitlab.com/gitlab-org/gitlab/-/issues/433324)