passport.js - How do I allow email as an alternative to username while authenticating with PassportJS? -

how allow uses log in using username or email? authenticating using passport local strategy connected mongoose schema. currently, i'm able authenticate username (and password, of course). /login route looks this:

// lib/authenticate.js router.post('/login', (req, res) => {   passport.authenticate('local')(req, res, () => {     // logged in, return user info token     if (req.user) {       const userdata = json.stringify(req.user);             let token = jwt.sign({                 username: req.user.username,                 firstname: req.user.firstname,                 lastname: req.user.lastname,                 email: req.user.email,                 img: req.user.img,             }, process.env.jwt_secret);             res.cookie('token', token);       return res.send(userdata);     }     // otherwise return error     return res.send(json.stringify({ error: 'there error logging in' }));   }); }); 

the mongoose model passport hooked is:

// /models/user.js const { mongoose } = require('../config/dbconfig');  const schema = mongoose.schema; const passportlocalmongoose = require('passport-local-mongoose');  const user = new schema({   username: {         type: string,         lowercase: true,         required: true,     },   password: {         type: string,         select: false,         required: true,     },   firstname: {         type: string,         required: true,     },   lastname: {         type: string,         required: true,     },   email: {         type: string,         lowercase: true,         required: true,     },   img: {         type: string,     }, }, { timestamps: true });  user.plugin(passportlocalmongoose);  module.exports = mongoose.model('user', user); 

the auth script above improvisation on 1 got off passportjs tutorial , works fine still struggling see it's doing authentication. mean how know match payload against right fields (in case, username , password)? don't see explicit field mapping anywhere in script. automagic going on here?

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