[Foowy]

Summary

Adds a sign-in button to the login page for each plugin that advertises a login-method feature, so plugin-provided sign-in (for example OIDC/SSO) can be offered without a WebUI change per plugin.

Draft: the login-method feature contract below is a proposal and I would like feedback on it before it settles.

Changes

• LoginPage.tsx: shows an "or" divider and a "Sign in with {displayName}" button under Login for every login method. Clicking it navigates the browser to the plugin's loginUrl, passing the current redirectTo as returnUrl.
• src/core/utilities/loginMethods.ts: picks the anonymous login-method features out of the feature list and validates them. Only a loginUrl that is a path on the same server is accepted (no absolute urls, //host, backslashes or other schemes), since it comes from plugin metadata.
• plugin/queries.ts, types/api/plugin.ts: usePluginFeaturesQuery for GET Plugin/Features and the PluginFeatureType type. The query only runs once the server is Started.
• tests/core/utilities/loginMethods.test.ts: covers the filtering, the rejected urls and the returnUrl handling.

Proposed contract

An anonymous plugin feature named login-method with metadata:

• displayName: text for the button
• loginUrl: a path on this server that starts the sign-in and ends by sending the browser to returnUrl (default /webui) with a session stored in sessionStorage.state.apiSession

A plugin that implements it is Foowy/Shoko.Plugin.Oidc.

Checked in a headless browser against a build of this branch and that plugin: the button shows on the login page, signs in through an external provider and lands on the dashboard with a session.