* feat(server): add ExtAuth logout URL configuration (#4467)
When external authentication (reverse proxy auth) is active, the Logout
button is hidden because authentication is managed externally. Many
external auth services (Authelia, Authentik, Keycloak) provide a logout
URL that can terminate the session.
Add `ExtAuth.LogoutURL` config option that, when set, shows the Logout
button in the UI and redirects the user to the external auth provider's
logout endpoint instead of the Navidrome login page.
* feat(server): add validation for ExtAuth logout URL configuration
* feat(server): refactor ExtAuth logout URL validation to a reusable function
* fix(configuration): rename URL validation functions for consistency
Signed-off-by: Deluan <deluan@navidrome.org>
* fix(configuration): rename URL validation functions for consistency
Signed-off-by: Deluan <deluan@navidrome.org>
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Signed-off-by: Deluan <deluan@navidrome.org>