in nuxt, where do i specify the context's types?

export default defineEventHandler(async (event) => {
  const config = useRuntimeConfig();

  const session_id = getCookie(event, 'session_id');
  let ctx: SessionContext | null = null;

  if (session_id) {
    const s: SessionContext = await validateSession(session_id);
    if (s.user === null) {
      deleteCookie(event, 'session');
    }
  }
  // how do i access this within my nuxt app?
  // this is only on the server side right?
  event.context.session = ctx;

  if (!ctx && config.authRoutes.includes(event.path)) {
    sendRedirect(event, '/login', 302);
  }
});