Express Session expiry vs First Time Loging in

Question

How to differentiate whether the session expired or is it the first time logging in.

I am setting the session like this and storing the data in express-mysql-session.

const sessionStore = new MySQLStore({}, connection);

// session
const adminSession = session({
  secret: process.env.ADMIN_SECRET,
  resave: false,
  saveUninitialized: false,
  store: sessionStore,
  name: "adminSession",
  cookie: {
    maxAge: 600000,
    secure: false,
  },
});
app.use("/api/admin", adminSession, adminRoutes);

//admin login
app.post("/api/admin/login",(req,res)=>{
    req.session.adminAuthenticated = true;
});

By simply checking if there is req.session.adminAuthenticated, I can know if admin is logged in or not. But how can I know if the admin had already logged in earlier but the session expired.
Any help with this.