Archive for the ‘REST API’ Category

JSON Web Token Tutorial: An Example in Laravel and AngularJS

Integrating Facebook Authentication in AngularJS App with Satellizer

With the arrival of feature-rich front-end frameworks such as AngularJS, more and more logic is being implemented on the front-end, such as data manipulation/validation, authentication, and more. Satellizer, an easy to use token-based authentication module for AngularJS, simplifies the process of implementing authentication mechanism in AngularJS, The library comes with built-in support for Google, Facebook, LinkedIn, Twitter, Instagram, GitHub, Bitbucket, Yahoo, Twitch, and Microsoft (Windows Live) accounts.

Integrating Facebook Login in AngularJS App with Satellizer

In this article, we will build a very simple webapp similar to the one here which allows you to login and see current user’s information.

Authentication vs Authorization

These are 2 scary words that you often encounter once your app starts integrating a user system. According to Wikipedia:

Authentication is the act of confirming the truth of an attribute of a single piece of data (a datum) claimed true by an entity.

Authorization is the function of specifying access rights to resources related to information security and computer security in general and to access control in particular.

In layman terms, let’s take an example of a blog website with some people working on it. The bloggers write articles and the manager validates the content. Each person can authenticate (login) into the system but their rights (authorisation) are different, so the blogger cannot validate content whereas the manager can.

Why Satellizer

You can create your own authentication system in AngularJS by following some tutorials such as this very detailed one: JSON Web Token Tutorial: An Example in Laravel and AngularJS. I suggest reading this article as it explains JWT (JSON Web Token) very well, and shows a simple way to implement authentication in AngularJS using directly the local storage and HTTP interceptors.

So why Satellizer? The principal reason is that it supports a handful of social network logins such as Facebook, Twitter, etc. Nowadays, especially for websites used on mobile, typing username and password is quite cumbersome and users expect to be able to use your website with little hindrance by using social logins. As integrating the SDK of each social network and following their documentations is quite repetitive, it would be nice to support these social logins with minimal effort.

Moreover Satellizer is an active project on Github. Active is key here as these SDKs change quite frequently and you don’t want to read their documentation every now and then (anyone working with Facebook SDK knows how annoying it is)

AngularJS App with Facebook Login

This is where things start to become interesting.

We will build a web app that has regular login/register (i.e. using username, password) mechanism and supports social logins as well. This webapp is very simple as it has only 3 pages:

  • Home page: anyone can see
  • Login page: to enter username/password
  • Secret page: that only logged in users can see

For backend, we will use Python and Flask. Python and the framework Flask are quite expressive so I hope porting the code to other languages/frameworks will not be very hard. We will, of course, use AngularJS for front-end. And for the social logins, we will integrate with Facebook only as it is the most popular social network at this time.

Let’s start!

Step #1: Bootstrap Project

Here is how we will structure our code:

- app.py
- static/
	- index.html
- app.js
	- bower.json
	- partials/
		- login.tpl.html
		- home.tpl.html
		- secret.tpl.html

All the back-end code is in app.py. The front-end code is put in static/ folder. By default, Flask will automatically serve the contents of static/ folder. All the partial views are in static/partials/ and handled by the ui.router module.

To start coding the back-end, we’ll need Python 2.7.* and install the required libraries using pip. You can of course use virtualenv to isolate a Python environment. Below is the list of required Python modules to put in requirements.txt:

Flask==0.10.1
PyJWT==1.4.0
Flask-SQLAlchemy==1.0
requests==2.7.0

To install all these dependencies:

pip install -r requirements.txt

In app.py we have some initial code to bootstrap Flask (import statements are omitted for brevity):

app = Flask(__name__)

@app.route('/')
def index():
    return flask.redirect('/static/index.html')

if __name__ == '__main__':
    app.run(debug=True)

Next we init bower and install AngularJS and ui.router:

bower init # here you will need to answer some question. when in doubt, just hit enter :)
bower install angular angular-ui-router --save # install and save these dependencies into bower.json

Once these libraries are installed, we need to include AngularJS and ui-router in index.html and create routings for 3 pages: home, login, and secret.

<body ng-app="DemoApp">

<a ui-sref="home">Home</a>
<a ui-sref="login">Login</a>
<a ui-sref="secret">Secret</a>
<div ui-view></div>

<script src="bower_components/angular/angular.min.js"></script>
<script src="bower_components/angular-ui-router/release/angular-ui-router.min.js"></script>
<script src="main.js"></script>
</body>

Below is the code that we need in main.js to configure routing:

var app = angular.module('DemoApp', ['ui.router']);

app.config(function ($stateProvider, $urlRouterProvider) {
  $stateProvider
    .state('home', {
      url: '/home',
      templateUrl: 'partials/home.tpl.html'
    })
    .state('secret', {
      url: '/secret',
      templateUrl: 'partials/secret.tpl.html',
    })
    .state('login', {
      url: '/login',
      templateUrl: 'partials/login.tpl.html'
    });
  $urlRouterProvider.otherwise('/home');

});

At this point if you run the server python app.py, you should have this basic interface at http://localhost:5000

The links Home, Login, and Secret should work at this point and show the content of the corresponding templates.

Congratulation, you just finished setting up the skeleton! If you encounter any error, please check out thecode on GitHub

Step #2: Login and Register

At the end of this step, you’ll have a webapp that you can register/login using email and password.

The first step is to configure the backend. We need a User model and a way to generate the JWT token for a given user. The User model shown below is really simplified and does not perform even any basic checks such as if field email contains “@”, or if field password contains at least 6 characters, etc.

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    email = db.Column(db.String(100), nullable=False)
    password = db.Column(db.String(100))

    def token(self):
        payload = {
            'sub': self.id,
            'iat': datetime.utcnow(),
            'exp': datetime.utcnow() + timedelta(days=14)
        }
        token = jwt.encode(payload, app.config['TOKEN_SECRET'])
        return token.decode('unicode_escape')

We use the jwt module in python to generate the payload part in JWT. The iat and exp part correspond to the timestamp that token is created and expired. In this code, the token will be expired in 2 weeks.

After the model User was created, we can add the “login” and “register” endpoints. The code for both are quite similar, so here I will just show the “register” part. Please note that by default, Satellizer will call the endpoints /auth/login and /auth/signup for the “login” and “register” respectively.

@app.route('/auth/signup', methods=['POST'])
def signup():
    data = request.json

    email = data["email"]
    password = data["password"]

    user = User(email=email, password=password)
    db.session.add(user)
    db.session.commit()

    return jsonify(token=user.token())

Let’s check the endpoint using curl first:

curl localhost:5000/auth/signup -H "Content-Type: application/json" -X POST -d '{"email":"[email protected]","password":"xyz"}'

The result should look like this:

{
  "token": "very long string…."
}

Now that the back-end part is ready, let’s attack the front-end! First, we need to install satellizer and add it as a dependency in main.js:

bower install satellizer --save

Add satellizer as dependency:

var app = angular.module('DemoApp', ['ui.router', 'satellizer']);

Login and signup in satellizer is actually quite simple in comparison to all the setup until now:

$scope.signUp = function () {
    $auth
      .signup({email: $scope.email, password: $scope.password})
      .then(function (response) {
        // set the token received from server
        $auth.setToken(response);
        // go to secret page
        $state.go('secret');
      })
      .catch(function (response) {
        console.log("error response", response);
      })
  };

If you have any difficulty setting up the code, you can take a look at the code on GitHub.

Step #3: But Secret View Is Not Really Secret, Because Anyone Can See It!

Yes, that is correct! Until now, anyone can go to secret page without logging in.

It’s time to add some interceptor in AngularJS to make sure that if someone goes to secret page and if this user is not logged in, they will be redirected to the login page.

First, we should add a flag requiredLogin to distinguish secret page from other ones.

    .state('secret', {
      url: '/secret',
      templateUrl: 'partials/secret.tpl.html',
      controller: 'SecretCtrl',
      data: {requiredLogin: true}
    })

The “data” part will be used in the $stateChangeStart event which is fired each time the routing changes:

app.run(function ($rootScope, $state, $auth) {
  $rootScope.$on('$stateChangeStart',
    function (event, toState) {
      var requiredLogin = false;
      // check if this state need login
      if (toState.data && toState.data.requiredLogin)
        requiredLogin = true;
      
      // if yes and if this user is not logged in, redirect him to login page
      if (requiredLogin && !$auth.isAuthenticated()) {
        event.preventDefault();
        $state.go('login');
      }
    });
});

Now, the user cannot go directly to the secret page without logging in. Hooray!

As usual, the code of this step can be found here.

Step #4: It’s Time to Get Something Really Secret!

At this moment, there’s nothing really secret in the secret page. Let’s put something personal there.

This step starts by creating an endpoint in the back-end which is only accessible for an authenticated user, such as having a valid token. The endpoint /user below returns the user_id and email of the user corresponding to the token.

@app.route('/user')
def user_info():
    # the token is put in the Authorization header
    if not request.headers.get('Authorization'):
        return jsonify(error='Authorization header missing'), 401
    
    # this header looks like this: “Authorization: Bearer {token}”
    token = request.headers.get('Authorization').split()[1]
    try:
        payload = jwt.decode(token, app.config['TOKEN_SECRET'])
    except DecodeError:
        return jsonify(error='Invalid token'), 401
    except ExpiredSignature:
        return jsonify(error='Expired token'), 401
    else:
        user_id = payload['sub']
        user = User.query.filter_by(id=user_id).first()
        if user is None:
            return jsonify(error='Should not happen ...'), 500
        return jsonify(id=user.id, email=user.email), 200
    return jsonify(error="never reach here..."), 500

Again, we make use of the module jwt to decode the JWT token included in the ‘Authorization’ header and to handle the case when the token is expired or not valid.

Let’s test this endpoint using curl. First, we need to get a valid token:

curl localhost:5000/auth/signup -H "Content-Type: application/json" -X POST -d '{"email":"[email protected]","password":"xyz"}'

Then with this token:

curl localhost:5000/user -H "Authorization: Bearer {put the token here}"

Which gives this result:

{
  "email": "[email protected]",
  "id": 1
}

Now we need to include this endpoint in the Secret Controller. This is quite simple as we just need to call the endpoint using the regular $http module. The token is automatically inserted to the header by Satellizer, so we don’t need to bother with all the details of saving the token and then putting it in the right header.

  getUserInfo();

  function getUserInfo() {
    $http.get('/user')
      .then(function (response) {
        $scope.user = response.data;
      })
      .catch(function (response) {
        console.log("getUserInfo error", response);
      })
  }

Finally, we have something truly personal in the secret page!

The code of this step is on GitHub.

Step #5: Facebook Login with Satellizer

A nice thing about Satellizer, as mentioned at the beginning, is it makes integrating social login a lot easier. At the end of this step, users can login using their Facebook account!

First thing to do is to create an application on Facebook developers page in order to have an application_idand a secret code. Please follow developers.facebook.com/docs/apps/register to create a Facebook developer account if you don’t have one already and create a website app. After that, you will have the application ID and application secret as in the screenshot below.

Once the user chooses to connect with Facebook, Satellizer will send an authorization code to the endpoint/auth/facebook. With this authorization code, the back-end can retrieve an access token from Facebook/oauth endpoint that allows the call to Facebook Graph API to get user information such as location, user_friends, user email, etc.

We also need to keep track of whether a user account is created with Facebook or through regular signup. To do so, we add facebook_id to our User model.

facebook_id = db.Column(db.String(100)) 

The facebook secret is configured via env variables FACEBOOK_SECRET that we add to app.config.

app.config['FACEBOOK_SECRET'] = os.environ.get('FACEBOOK_SECRET')

So to launch the app.py, you should set this env variable:

FACEBOOK_SECRET={your secret} python app.py

Here is the method which handles Facebook logins. By default Satellizer will call the endpoint /auth/facebook.

@app.route('/auth/facebook', methods=['POST'])
def auth_facebook():
    access_token_url = 'https://graph.facebook.com/v2.3/oauth/access_token'
    graph_api_url = 'https://graph.facebook.com/v2.5/me?fields=id,email'

    params = {
        'client_id': request.json['clientId'],
        'redirect_uri': request.json['redirectUri'],
        'client_secret': app.config['FACEBOOK_SECRET'],
        'code': request.json['code']
    }

    # Exchange authorization code for access token.
    r = requests.get(access_token_url, params=params)
    # use json.loads instead of urlparse.parse_qsl
    access_token = json.loads(r.text)

    # Step 2. Retrieve information about the current user.
    r = requests.get(graph_api_url, params=access_token)
    profile = json.loads(r.text)

    # Step 3. Create a new account or return an existing one.
    user = User.query.filter_by(facebook_id=profile['id']).first()
    if user:
        return jsonify(token=user.token())

    u = User(facebook_id=profile['id'], email=profile['email'])
    db.session.add(u)
    db.session.commit()
    return jsonify(token=u.token())

To send a request to the Facebook server, we use the handy module requests. Now the difficult part on the back-end is done. On the front-end, adding Facebook login is quite simple. First, we need to tell Satellizer ourfacebook_id by adding this code into app.config function:

$authProvider.facebook({
    clientId: {your facebook app id},
    // by default, the redirect URI is http://localhost:5000
    redirectUri: 'http://localhost:5000/static/index.html'
  });

To login using Facebook, we can just call:

$auth.authenticate(“facebook”)

As usual, you can check the code on GitHub

At this time, the webapp is complete in terms of functionality. The user can login/register using regular email and password or by using Facebook. Once logged in, the user can see his secret page.

Make a Pretty Interface

The interface is not very pretty at this point, so let’s add a little bit of Bootstrap for the layout and the angular toaster module to handle an error message nicely, such as when login fails.

The code for this beautifying part can be found here.

Conclusion

This article shows a step-by-step integration of Satellizer in a (simple) AngularJS webapp. With Satellizer, we can easily add other social logins such as Twitter, Linkedin, and more. The code on the front-end is quite the same as in the article. However, the back-end varies as social network SDKs have different endpoints with different protocols. You can take a look at https://github.com/sahat/satellizer/blob/master/examples/server/python/app.py which contains examples for Facebook, Github, Google, Linkedin, Twiter and Bitbucket. When in doubt, you should take a look at the documentation on https://github.com/sahat/satellizer.

This article was written by Son Nguyen Kim, a Toptal freelance developer.

REST Security with JWT using Java and Spring Security

The following article is a guest post from Toptal. Toptal is an elite network of freelancers that enables businesses to connect with the top 3% of software engineers and designers in the world.

Security

Security is the enemy of convenience, and vice versa. This statement is true for any system, virtual or real, from the physical house entrance to web banking platforms. Engineers are constantly trying to find the right balance for the given use case, leaning to one side or the other. Usually, when a new threat appears, we move towards security and away from convenience. Then, we see if we can recover some lost convenience without reducing the security too much. Moreover, this vicious circle goes on forever.

Security vs. convenience

Security is the enemy of convenience, and vice versa.

Let’s try to see where REST services currently stand regarding security and convenience. REST (which stands for Representational State Transfer) services started off as an extremely simplified approach to Web Services that had huge specifications and cumbersome formats, such as WSDL for describing the service, or SOAP for specifying the message format. In REST, we have none of those. We can describe the REST service in a plain text file and use any message format we want, such as JSON, XML or even plain text again. The simplified approach was applied to the security of REST services as well; no defined standard imposes a particular way to authenticate users.

Although REST services do not have much specified, an important one is the lack of state. It means the server does not keep any client state, with sessions as a good example. Thus, the server replies to each request as if it was the first the client has made. However, even now, many implementations still use cookie based authentication, which is inherited from standard website architectural design. The stateless approach of REST makes session cookies inappropriate from the security standpoint, but nevertheless, they are still widely used. Besides ignoring the required statelessness, simplified approach came as an expected security trade-off. Compared to the WS-Security standard used for Web Services, it is much easier to create and consume REST services, hence convenience went through the roof. The trade-off is pretty slim security; session hijacking and cross-site request forgery (XSRF) are the most common security issues.

In trying to get rid of client sessions from the server, some other methods have been used occasionally, such as Basic or Digest HTTP authentication. Both use an Authorization header to transmit user credentials, with some encoding (HTTP Basic) or encryption (HTTP Digest) added. Of course, they carried the same flaws found in websites: HTTP Basic had to be used over HTTPS since username and password are sent in easily reversible base64 encoding, and HTTP Digest forced the use of obsolete MD5 hashing that is proven to be insecure.

Finally, some implementations used arbitrary tokens to authenticate clients. This option seems to be the best we have, for now. If implemented properly, it fixes all the security problems of HTTP Basic, HTTP Digest or session cookies, it is simple to use, and it follows the stateless pattern.

However, with such arbitrary tokens, there’s little standard involved. Every service provider had his or her idea of what to put in the token, and how to encode or encrypt it. Consuming services from different providers required additional setup time, just to adapt to the specific token format used. The other methods, on the other hand (session cookie, HTTP Basic and HTTP Digest) are well known to developers, and almost all browsers on all devices work with them out of the box. Frameworks and languages are ready for these methods, having built-in functions to deal with each seamlessly.

JWT

JWT (shortened from JSON Web Token) is the missing standardization for using tokens to authenticate on the web in general, not only for REST services. Currently, it is in draft status as RFC 7519. It is robust and can carry a lot of information, but is still simple to use even though its size is relatively small. Like any other token, JWT can be used to pass the identity of authenticated users between an identity provider and a service provider (which are not necessarily the same systems). It can also carry all the user’s claim, such as authorization data, so the service provider does not need to go into the database or external systems to verify user roles and permissions for each request; that data is extracted from the token.

Here is how JWT is designed to work:

JWT flow

  • Clients logs in by sending their credentials to the identity provider.
  • The identity provider verifies the credentials; if all is OK, it retrieves the user data, generates a JWT containing user details and permissions that will be used to access the services, and it also sets the expiration on the JWT (which might be unlimited).
  • Identity provider signs, and if needed, encrypts the JWT and sends it to the client as a response to the initial request with credentials.
  • Client stores the JWT for a limited or unlimited amount of time, depending on the expiration set by the identity provider.
  • Client sends the stored JWT in an Authorization header for every request to the service provider.
  • For each request, the service provider takes the JWT from the Authorization header and decrypts it, if needed, validates the signature, and if everything is OK, extracts the user data and permissions. Based on this data solely, and again without looking up further details in the database or contacting the identity provider, it can accept or deny the client request. The only requirement is that the identity and service providers have an agreement on encryption so that service can verify the signature or even decrypt which identity was encrypted.

This flow allows for great flexibility while still keeping things secure and easy to develop. By using this approach, it is easy to add new server nodes to the service provider cluster, initializing them with only the ability to verify the signature and decrypt the tokens by providing them a shared secret key. No session replication, database synchronization or inter-node communication is required. REST in its full glory.

The main difference between JWT and other arbitrary tokens is the standardization of the token’s content. Another recommended approach is to send the JWT token in the Authorization header using the Bearer scheme. The content of the header should look like this:

Authorization: Bearer <token>

Implementation

For REST services to work as expected, we need a slightly different authorization approach compared to classic, multi-page websites.

Instead of triggering the authentication process by redirecting to a login page when a client requests a secured resource, the REST server authenticates all requests using the data available in the request itself, the JWT token in this case. If such an authentication fails, redirection makes no sense. The REST API simply sends an HTTP code 401 (Unauthorized) response and clients should know what to do; for example, a browser will show a dynamic div to allow the user to supply the username and password.

On the other hand, after a successful authentication in classic, multi-page websites, the user is redirected by using HTTP code 301 (Moved permanently), usually to a home page or, even better, to the page the user initially requested that triggered the authentication process. With REST, again this makes no sense. Instead we would simply continue with the execution of the request as if the resource was not secured at all, return HTTP code 200 (OK) and expected response body.

Spring Security

REST Security with JWT, Spring Security and Java

Now, let’s see how can we implement the JWT token based REST API using Java and Spring, while trying to reuse the Spring security default behavior where we can. As expected, Spring Security framework comes with many ready to plug-in classes that deal with “old” authorization mechanisms: session cookies, HTTP Basic, and HTTP Digest. However, it lacks the native support for JWT, and we need to get our hands dirty to make it work.

First, we start with the usual Spring Security filter definition in web.xml:

<filter>
	<filter-name>springSecurityFilterChain</filter-name>
	<filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
</filter>
<filter-mapping>
	<filter-name>springSecurityFilterChain</filter-name>
	<url-pattern>/*</url-pattern>
</filter-mapping>

Note that the name of the filter must be exactly springSecurityFilterChain for the rest of the Spring config to work out of the box.

Next comes the XML declaration of the Spring beans related to security. In order to simplify the XML, we will set the default namespace to security by adding xmlns="http://www.springframework.org/schema/security" to the root XML element. The rest of the XML looks like this:

    <global-method-security pre-post-annotations="enabled" />  (1)
    
    <http pattern="/api/login" security="none"/>   (2)
    <http pattern="/api/signup" security="none"/>

    <http pattern="/api/**" entry-point-ref="restAuthenticationEntryPoint" create-session="stateless"> (3)
        <csrf disabled="true"/>  (4)
        <custom-filter before="FORM_LOGIN_FILTER" ref="jwtAuthenticationFilter"/>  (5)
    </http>
    
    <beans:bean id="jwtAuthenticationFilter" class="com.toptal.travelplanner.security.JwtAuthenticationFilter">  (6)
        <beans:property name="authenticationManager" ref="authenticationManager" />
        <beans:property name="authenticationSuccessHandler" ref="jwtAuthenticationSuccessHandler" />  (7)
    </beans:bean>

    <authentication-manager alias="authenticationManager">
        <authentication-provider ref="jwtAuthenticationProvider" />  (8)
    </authentication-manager>
  • (1) In this line, we activate @PreFilter@PreAuthorize@PostFilter@PostAuthorize annotations on any spring beans in the context.
  • (2) We define the login and signup endpoints to skip security; even “anonymous” should be able to do these two operations.
  • (3) Next, we define the filter chain applied to all requests while adding two important configs: Entry point reference and setting the session creation to stateless (we do not want the session created for security purposes as we are using tokens for each request).
  • (4) We do not need csrf protection because our tokens are immune to it.
  • (5) Next, we plug in our special authentication filter within the Spring’s predefined filter chain, just before the form login filter.
  • (6) This bean is the declaration of our authentification filter; since it is extending Spring’s AbstractAuthenticationProcessingFilter, we need to declare it in XML to wire its properties (auto wire does not work here). We will explain later what the filter does.
  • (7) The default success handler of AbstractAuthenticationProcessingFilter is not good enough for REST purposes because it redirects the user to a success page; that is why we set our own here.
  • (8) The declaration of the provider created by the authenticationManager is used by our filter to authenticate users.

Now let’s see how we implement the specific classes declared in the XML above. Note that Spring will wire them for us. We start with the simplest ones.

RestAuthenticationEntryPoint.java

public class RestAuthenticationEntryPoint implements AuthenticationEntryPoint {

    @Override
    public void commence(HttpServletRequest request, HttpServletResponse response, AuthenticationException authException) throws IOException {
        // This is invoked when user tries to access a secured REST resource without supplying any credentials
        // We should just send a 401 Unauthorized response because there is no 'login page' to redirect to
        response.sendError(HttpServletResponse.SC_UNAUTHORIZED, "Unauthorized");
    }
}

As explained above, this class just returns HTTP code 401 (Unauthorized) when authentication fails, overriding default Spring’s redirecting.

JwtAuthenticationSuccessHandler.java

public class JwtAuthenticationSuccessHandler implements AuthenticationSuccessHandler {

    @Override
    public void onAuthenticationSuccess(HttpServletRequest request, HttpServletResponse response, Authentication authentication) {
        // We do not need to do anything extra on REST authentication success, because there is no page to redirect to
    }

}

This simple override removes the default behavior of a successful authentication (redirecting to home or any other page the user requested). If you are wondering why we do not need to override the AuthenticationFailureHandler, it is because default implementation will not redirect anywhere if its redirect URL is not set, so we just avoid setting the URL, which is good enough.

JwtAuthenticationFilter.java

public class JwtAuthenticationFilter extends AbstractAuthenticationProcessingFilter {

    public JwtAuthenticationFilter() {
        super("/**");
    }

    @Override
    protected boolean requiresAuthentication(HttpServletRequest request, HttpServletResponse response) {
        return true;
    }

    @Override
    public Authentication attemptAuthentication(HttpServletRequest request, HttpServletResponse response) throws AuthenticationException {

        String header = request.getHeader("Authorization");

        if (header == null || !header.startsWith("Bearer ")) {
            throw new JwtTokenMissingException("No JWT token found in request headers");
        }

        String authToken = header.substring(7);

        JwtAuthenticationToken authRequest = new JwtAuthenticationToken(authToken);

        return getAuthenticationManager().authenticate(authRequest);
    }

    @Override
    protected void successfulAuthentication(HttpServletRequest request, HttpServletResponse response, FilterChain chain, Authentication authResult)
            throws IOException, ServletException {
        super.successfulAuthentication(request, response, chain, authResult);

        // As this authentication is in HTTP header, after success we need to continue the request normally
        // and return the response as if the resource was not secured at all
        chain.doFilter(request, response);
    }
}

This class is the entry point of our JWT authentication process; the filter extracts the JWT token from the request headers and delegates authentication to the injected AuthenticationManager. If the token is not found, an exception is thrown that stops the request from processing. We also need an override for successful authentication because the default Spring flow would stop the filter chain and proceed with a redirect. Keep in mind we need the chain to execute fully, including generating the response, as explained above.

JwtAuthenticationProvider.java

public class JwtAuthenticationProvider extends AbstractUserDetailsAuthenticationProvider {

    @Autowired
    private JwtUtil jwtUtil;

    @Override
    public boolean supports(Class<?> authentication) {
        return (JwtAuthenticationToken.class.isAssignableFrom(authentication));
    }

    @Override
    protected void additionalAuthenticationChecks(UserDetails userDetails, UsernamePasswordAuthenticationToken authentication) throws AuthenticationException {
    }

    @Override
    protected UserDetails retrieveUser(String username, UsernamePasswordAuthenticationToken authentication) throws AuthenticationException {
        JwtAuthenticationToken jwtAuthenticationToken = (JwtAuthenticationToken) authentication;
        String token = jwtAuthenticationToken.getToken();

        User parsedUser = jwtUtil.parseToken(token);

        if (parsedUser == null) {
            throw new JwtTokenMalformedException("JWT token is not valid");
        }

        List<GrantedAuthority> authorityList = AuthorityUtils.commaSeparatedStringToAuthorityList(parsedUser.getRole());

        return new AuthenticatedUser(parsedUser.getId(), parsedUser.getUsername(), token, authorityList);
    }

}

In this class, we are using Spring’s default AuthenticationManager, but we inject it with our own AuthenticationProvider that does the actual authentication process. To implement this, we extend the AbstractUserDetailsAuthenticationProvider, which requires us only to return UserDetails based on the authentication request, in our case, the JWT token wrapped in the JwtAuthenticationToken class. If the token is not valid, we throw an exception. However, if it is valid and decryption by JwtUtil is successful, we extract the user details (we will see exactly how in the JwtUtil class), without accessing the database at all. All the information about the user, including his or her roles, is contained in the token itself.

JwtUtil.java

public class JwtUtil {

    @Value("${jwt.secret}")
    private String secret;

    /**
     * Tries to parse specified String as a JWT token. If successful, returns User object with username, id and role prefilled (extracted from token).
     * If unsuccessful (token is invalid or not containing all required user properties), simply returns null.
     * 
     * @param token the JWT token to parse
     * @return the User object extracted from specified token or null if a token is invalid.
     */
    public User parseToken(String token) {
        try {
            Claims body = Jwts.parser()
                    .setSigningKey(secret)
                    .parseClaimsJws(token)
                    .getBody();

            User u = new User();
            u.setUsername(body.getSubject());
            u.setId(Long.parseLong((String) body.get("userId")));
            u.setRole((String) body.get("role"));

            return u;

        } catch (JwtException | ClassCastException e) {
            return null;
        }
    }

    /**
     * Generates a JWT token containing username as subject, and userId and role as additional claims. These properties are taken from the specified
     * User object. Tokens validity is infinite.
     * 
     * @param u the user for which the token will be generated
     * @return the JWT token
     */
    public String generateToken(User u) {
        Claims claims = Jwts.claims().setSubject(u.getUsername());
        claims.put("userId", u.getId() + "");
        claims.put("role", u.getRole());

        return Jwts.builder()
                .setClaims(claims)
                .signWith(SignatureAlgorithm.HS512, secret)
                .compact();
    }
}

Finally, JwtUtil class is in charge of parsing the token into User object and generating the token from the User object. It is straightforward since it uses the jjwt library to do all the JWT work. In our example, we simply store the username, user ID and user roles in the token. We could also store more arbitrary stuff and add more security features, such as the token’s expiration. Parsing of the token is used in the AuthenticationProvider as shown above. The generateToken() method is called from login and signup REST services, which are unsecured and will not trigger any security checks or require a token to be present in the request. In the end, it generates the token that will be returned to the clients, based on the user.

Conclusion

Although the old, standardized security approaches (session cookie, HTTP Basic, and HTTP Digest) will work with REST services as well, they all have problems that would be nice to avoid by using a better standard. JWT arrives just in time to save the day, and most importantly it is very close to becoming an IETF standard.

JWT’s main strength is handling user authentication in a stateless, and therefore scalable, way, while keeping everything secure with up-to-date cryptography standards. Storing claims (user roles and permissions) in the token itself creates huge benefits in distributed system architectures where the server that issues the request has no access to the authentication data source.