ui: login page — SSO button + oidc_error banner

internal/server/ui/ui.go

@@ -56,6 +56,19 @@ type ViewData struct {
 	// today; other pages can adopt the same field.
 	Error string
 
+	// OIDCEnabled is true when the server has an OIDC provider
+	// configured. The login page uses it to show the SSO button.
+	OIDCEnabled bool
+
+	// OIDCDisplayName is the human-readable label for the OIDC
+	// provider (e.g. "Authelia"). Shown on the SSO button.
+	OIDCDisplayName string
+
+	// OIDCError holds an error code returned via ?oidc_error=… after
+	// a failed OIDC callback. The login page maps it to a user-facing
+	// message.
+	OIDCError string
+
 	// Page carries page-specific data. Concrete type is the page's
 	// own struct.
 	Page any