const jwt = require('jsonwebtoken’);

app.post('/login', (req,res) => {
    let username = req.body.username
    let password = req.body.password
   bcrypt.compare(password, hash,(err, result) => {
      if(result){
         let token =
             jwt.sign({username:username},'secretkey')
         res.json({token:token)
       } else{
          res.status(403)
             .send({token:null})
       }
    })
})