How do I make a user access the register page and the login page using joi without using ejs or html

Question

I am stuck in making a user to access the register and login page in joi without using ejs or html. Below are the codes

const express = require("express");
const Joi = require("joi");



const app = express();



const schema = Joi.object({
email: Joi.string().email().required(),
password: Joi.string().min(4).alphanum().required(),
firstname: Joi.string().alphanum().required(),
lastname: Joi.string().alphanum().required()
})

app.post("/register", async(req,res) => {
if(err) {
    console.log(err);
} else{
    res.send("Success");
}
try{
    const value = await schema.validateAsync({
        email:req.body.email,
        password: req.body.password,
        firstname: req.body.firstname,
        lastname: req.body.lastname
    })
    } catch(e){
    console.log(e);
    }
 })

app.listen(3000, function(){
console.log("Listening on port 3000");
})

How do I also create a protected route that only authenticated users can use it