chore: import upstream snapshot with attribution

apps/webapp/app/services/authUser.ts

@@ -0,0 +1,11 @@
+export type AuthUser = {
+  userId: string;
+  // Present only when the session was established via SSO. Carries the
+  // minimum the periodic re-validation hook needs to ask the IdP whether
+  // the session is still valid. Signed into the session cookie, so it's
+  // tamper-proof. Absent ⇒ non-SSO session ⇒ never revalidated.
+  sso?: {
+    idpOrgId: string;
+    connectionId: string;
+  };
+};