implementing refresh-tokens with angular and express-jwt

Question

I want to implement the Sliding expiration concept with json web tokens using angular, nodejs and express-jwt. I'm a little confused on how to do this, and am struggling to find any example of refresh tokens or and other material relating to sessions with these technologies/frameworks.

A few options I was thinking of were

• Generating a new token with each request after the initial login
• Keeping track of issued token on the server side along

But I'm honestly not sure, please help

Answer 1

I managed to implement this scenario.

What I've done...

On the server:

-Enable an API endpoint for signin. This endpoint will respond with the Json Web Token in the header. The client side has to catch it (with $http interceptors) and save it (I use local storage). The client will also manage the refreshed tokens sent by the server.

-On every request to the server configure a middleware in express to validate the token. At first I tried express-jwt module but jsonwebtoken was the right one for me.

For specific routes you may want to disable the middleware. In this case signin and signout.

var jwtCheck = auth.verifyJWT;
jwtCheck.unless = unless;
app.use('/api', jwtCheck.unless({path: [
    '/api/auth/signin',
    '/api/auth/signout'
]}));

-The middleware verifyJWT always responds with a token in the header. If the token needs to be refreshed a refreshed function is called.

jwtLib is my own library where the code lives to create, refresh and fetch jwt tokens.

function(req, res, next) {
    var newToken,
        token = jwtLib.fetch(req.headers);

    if(token) {
        jwt.verify(token, config.jwt.secret, {
            secret: config.jwt.secret
        }, function(err, decoded) {
            if(err) {
                return res.status(401).send({
                    message: 'User token is not valid'
                });
            }
            //Refresh: If the token needs to be refreshed gets the new refreshed token
            newToken = jwtLib.refreshToken(decoded);
            if(newToken) {
                // Set the JWT refreshed token in http header
                res.set('Authorization', 'Bearer ' + newToken);
                next();
            } else {
                res.set('Authorization', 'Bearer ' + token);
                next();
            }
        });
    } else {
        return res.status(401).send({
            message: 'User token is not present'
        });
    }
};

-The refresh function (jwtLib). As argument needs a decoded token, see above that jsonwebtoken resolve a decoded when call to jwt.verify().

If you create during signin a token with an expiration of 4 hours and have a refresh expiration of 1 h (1 * 60 * 60 = 3600 secs) that means that the token will be refreshed if the user has been inactive for 3 hours or more, but not for more than 4 hours, because the verify process would fail in this case (1 hour window of refreshing). This avoids generating a new token on each request, only if the token will expire in this time window.

module.exports.refreshToken = function(decoded) {
    var token_exp,
        now,
        newToken;

    token_exp = decoded.exp;
    now = moment().unix().valueOf();

    if((token_exp - now) < config.jwt.TOKEN_REFRESH_EXPIRATION) {
        newToken = this.createToken(decoded.user);
        if(newToken) {
            return newToken;
        }
    } else {
       return null;
    }
};

On the client (Angularjs):

-Enable a client side for login. This calls the server endpoint. I use Http Basic Authentication encoded with base64. You can use base64 angular module to encode the email:password Note that on success I do not store the token on the localStorage or Cookie. This will be managed by the http Interceptor.

//Base64 encode Basic Authorization (email:password)
$http.defaults.headers.common.Authorization = 'Basic ' + base64.encode(credentials.email + ':' + credentials.password);
return $http.post('/api/auth/signin', {skipAuthorization: true});

-Configure the http interceptors to send the token to the server on every request and store the token on the response. If a refreshed token is received this one must be stored.

// Config HTTP Interceptors
angular.module('auth').config(['$httpProvider',
    function($httpProvider) {
        // Set the httpProvider interceptor
        $httpProvider.interceptors.push(['$q', '$location', 'localStorageService', 'jwtHelper', '$injector',
            function($q, $location, localStorageService, jwtHelper, $injector) {
                return {
                    request: function(config) {
                        var token = localStorageService.get('authToken');
                        config.headers = config.headers || {};

                        if (token && !jwtHelper.isTokenExpired(token)) {
                            config.headers.Authorization = 'Bearer ' + token;
                        }
                        return config;
                    },
                    requestError: function(rejection) {
                        return $q.reject(rejection);
                    },
                    response: function(response) {
                        //JWT Token: If the token is a valid JWT token, new or refreshed, save it in the localStorage
                        var Authentication = $injector.get('Authentication'),
                            storagedToken = localStorageService.get('authToken'),
                            receivedToken = response.headers('Authorization');
                        if(receivedToken) {
                            receivedToken = Authentication.fetchJwt(receivedToken);
                        }
                        if(receivedToken && !jwtHelper.isTokenExpired(receivedToken) && (storagedToken !== receivedToken)) {

                            //Save Auth token to local storage
                            localStorageService.set('authToken', receivedToken);
                        }
                        return response;
                    },
                    responseError: function(rejection) {
                        var Authentication = $injector.get('Authentication');
                        switch (rejection.status) {
                            case 401:
                                // Deauthenticate the global user
                                Authentication.signout();
                                break;
                            case 403:
                                // Add unauthorized behaviour
                                break;
                        }

                        return $q.reject(rejection);
                    }
                };
            }
        ]);
    }
]);