How to use the jwt-simple.decode function in jwt-simple

youtransfer.settings.get(function(err, settings) {

			var security = settings.security || {};
			var salt = security.encryptionKey || '';
			var user = jwt.decode(token, salt);

			// Check for JWT expiration
			var expires = new Date(user.exp);
			if(Date.compare(expires, new Date()) < 0) {
				user = null;
			}

			done(null, user);

		});

module.exports = function(req, res, next){
    if(!req.headers.authorization){
        return handleError();
    }

    var token = req.headers.authorization.split(' ')[1];

    var payload = jwt.decode(token, config.TOKEN_SECRET);

    if(!payload.sub){
        return handleError();
    }

    req.userId = payload.sub;
    next();
};

it('should allow construction of a capability token', function() {
        var c = new twilio.TaskRouterCapability('AC123', 'foobar', 'WS456', 'WK789');
        var token = c.generate();

        var decoded = jwt.decode(token, 'foobar');
        expect(decoded).toBeDefined();
        expect(decoded['iss']).toBe('AC123');
        expect(decoded['account_sid']).toBe('AC123');
        expect(decoded['channel']).toBe('WK789');
        expect(decoded['workspace_sid']).toBe('WS456');
        expect(decoded['worker_sid']).toBe('WK789');
        expect(decoded['version']).toBe('v1');
        expect(decoded['exp']).toEqual(Math.floor(new Date() / 1000) + 3600);
    });

function getProperty(propertyName, token) {
  var payload;
  try {
    payload = jwt.decode(token, null, true);
  }
  catch(err) {
    return false;
  }
  if (!payload[propertyName]) return false;
  return payload[propertyName];
}

function getJwt(token, secret){
  var jwtObject;
  try{
    jwtObject = jwt.decode(token, secret);
  }
  catch(e){
    return new ApiAuthRequestError({userMessage: 'access_token is invalid',statusCode: 401});
  }
  return jwtObject;
}

function decode(token: string, noVerify = false) {
		const decoded = jwt.decode(token, secret || '', !secret || noVerify);
		if (secret && !noVerify && !isValidTimestamp(decoded)) {
			throw new Error('invalid timestamp');
		}
		log('decode(token: %j, secret: %j) => %j', token, secret, decoded);
		return decoded;
	}

function decode( token, key, algorithm ) {

    try {

        return jwt.decode( token, key, false, algorithm );
    }
    catch( err ) {

        throw new AuthenticationFailureError( err.message );
    }
}

function decode( token, key, algorithm ) {

    try {

        return jwt.decode( token, key, false, algorithm );
    }
    catch( err ) {

        throw new AuthenticationFailureError( err.message );
    }
}