JWT decode returns null
<p>I'm new to Node.js, reading Node.js Essentials by Fabian Cook. When trying the code in authentication with JWT, I got an NULL from jwt.decode( token ), but the token can be parsed by the Debugger on jwt.io. What's wrong with the code?</p>

<pre><code>var Passport = require( 'passport' );
var LocalStrategy = require( 'passport-local' ).Strategy;
var Express = require( 'express' );
var BodyParser = require( 'body-parser' );
var jwt = require( 'jsonwebtoken' );
var Crypto = require ( 'crypto' );

var users = {
  zack: {
    username: 'zack',
    password: '1234',
    id: 1,
  },
  node: {
    username: 'node',
    password: '5678',
    id: 2,
  },
}

var localStrategy = new LocalStrategy({
      usernameField: 'username',
      passwordField: 'password',
    },
    function(username, password, done) {
      user = users[ username ];

      if ( user == null ) {
        return done( null, false, { message: 'Invalid user' } );
      };

      if ( user.password !== password ) {
        return done( null, false, { message: 'Invalid password' } );
      };

      done( null, user );
    }
  )

Passport.use( 'local', localStrategy );

var app = Express();
app.use( BodyParser.urlencoded( { extended: false } ) );
app.use( BodyParser.json() );
app.use( Passport.initialize() );

var generateToken = function( req, res ) {
  var payload = {
    id: user.id,
    username: user.username
  }
  var secret = user.secret || Crypto.randomBytes( 128 ).toString( 'base64' );
  var token = jwt.sign( payload, secret );
  user.secret = secret;
  return token;
};

var generateTokenHandler = function ( req, res ) {
  var user = req.user;
  var token = generateToken( user );
  res.send( token );
};

app.post(
  '/login',
  Passport.authenticate( 'local', { session: false } ),
  generateTokenHandler
);

var BearerStrategy = require( 'passport-http-bearer' ).Strategy;

var verifyToken = function( token, done ) {
  var payload = jwt.decode(token);
  if ( payload == null ){
    return done( null, false );
  }
  console.log(payload);
  var user = users[ payload.username ];
  if ( user == null ||
       user.id !== payload.id ||
       user.username !== payload.username ) {
    return done( null, false );
  }
  jwt.verify( token, user.secret, function ( error, decoded ) {
    if ( error || decoded == null ) {
      return done( error, false );
    }
    return done( null, user );
  })
}
var bearerStrategy = new BearerStrategy( verifyToken )


Passport.use( 'bearer', bearerStrategy );


app.get(
  '/userinfo',
  Passport.authenticate( 'bearer', { session: false } ),
  function ( req, res ) {
    var user = request.user;
    res.send( {
      id: user.id,
      username: user.username
    });
  }
);

app.listen( 3000, function() {
  console.log( 'Listening on 3000' );
});
</code></pre>

<p>Here is a token I got from the code F.Y.I.</p>

<pre><code>eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJpZCI6MSwidXNlcm5hbWUiOiJ6YWNrIiwiaWF0IjoxNDU5MDAzMTYxfQ.rhqOX0ICRvivNCwwLNsu5KizNPLQTKPVEqfCuxtII90~
</code></pre>