This post is about using JSON Web Token (JWT) with JAX-RS

It covers

Real quick intro to JWT

Shows how to use it with JAX-RS (for authentication) with an example

Also

demonstrates contextual state/information sharing feature provided by JAX-RS Request Filters and usage of custom Security Context in JAX-RS

uses the jose4j library for JWT creation and validation

Brief intro to JWT

A standard defined by RFC 7519

Used to exchange claims

Has a pre-defined structure

Anatomy of a JWT

It consists of three parts

Header: consists of info like signature mechanism, token type etc.

Body (Claims): the meat of the payload

Signature: signature of the contents to protect against tampered/malicious JWTs

These three components come together to form the actual token

Benefits

Useful for implementing Stateless authentication

Compact: less verbose compared to other counterparts like SAML)

Flexible: Although its backed by a standard, you are free to choose your signature, claim attributes etc.

Please note that…

JWT is not only an authentication mechanism. It’s more about information exchange & it’s usage is limited by your imagination

It’s signed, not encrypted: its contents can be picked up over the wire if you do not secure your transport layer (e.g. using HTTPS)

Using JWT with JAX-RS

Let’s look at an example of how we might use JWT in a JAX-RS based application. As stated earlier, this sample uses JWT as a stateless authentication token. The process is split into distinct steps

Getting hold of the JWT

Why do we need a JWT in the first place? It is because the JAX-RS resource is protected and its access is dependent on the presence of a JWT token within the HTTP request (this is achieved by a JAX-RS filter)

Think of JWT as a proxy to the actual username/password (or any other authentication criteria) for your application. You need to actually authenticate using the method required by your application in order to get access to the JWT. In this example, a successfully executed HTTP Basic authentication is the gateway to the token

This is what happens

The application executes a GET request to the URL http://<host>:<port>/<context-root>/auth/token with the HTTP Authorization header containing user credentials HTTP Basic authentication kicks in. This is enforced by the web.xml (snippet below) which ensures that any request to the /auth/* is not allowed to pass unauthenticated In case of a successful authentication, the JWT is returned in the HTTP response header

Here is an excerpt form the web.xml

Quick review of JWT creation code and its result

JWT in action

The JWT is sent by app in the subsequent request for the JAX-RS resource i.e.http:<host>:<port>/<context-root>/resources/books

The JAX-RS Container Request Filter kicks in – it checks for the presence of the JWT , verifies it. The verification process implicitly checks for presence of the required claim attributes as well as the signature validation

JWT verification snippet

It allows the request to go through in case of successful verification, otherwise, the filter returns a HTTP 401 Unauthorized response to the client

A container response filter ensures that the JWT is added as a part of the response header again. It only does so when the JWT verification was successful – this is made possible using the contextual state/information sharing feature provided by JAX-RS Request Filters

Other considerations

Choice of claim attributes

In this example, we just used the standard sub (subject) attribute in the claim. You are free to use others. I would highly recommend reading section 4 of the JWT RFC for deeper insight

JWT expiration

One should also consider expiring the JWT token after a finite time. You would need to

Make use of the exp claim attribute (standard)

claim attribute (standard) Think about refreshing the JWT token (after expiry)

Revisiting the Stateless paradigm..

Although the initial authentication was executed using HTTP Basic, the application does not rely on a Session ID for authorising subsequent requests from the same user. This has the following implications

There is no need to store the session ID on the server side

There is no need to sync this session ID to multiple application nodes in a cluster

As stated above, JWT is helping us with Stateless authentication (it is not very different from the HTTP protocol itself)

Our JWT contains all the required data (claim) for the conversation (in this case authentication)

We pass the token with each HTTP request (only to access resources which are protected by the JWT to begin with)

The application does not need to repetitively authenticate the user (via the username-password combo)

Now we can scale 🙂

You can have multiple instances (horizontally scaled across various nodes/clusters) of your JAX-RS service and yet you need not sync the state of the token between various nodes. If a subsequent request goes to different node than the previous request, the authentication will still happen (provided you pass the JWT token)

Using the sample project

If you want to play around with the example, please follow hese steps

Get the maven project and build it (same old maven clean install)

Deploy on a Java EE 7 container

Tweak your server security options to protect it using a realm named file and ensure that you include the members under the users group. Both these constraints are dictated by the web.xml descriptor (see above) – you can also choose to modify it as per your choice. Here is a snapshot from the Payara server

Issue a HTTP GET to http://localhost:8080/jax-rs-with-jwt/auth/token

Copy the token in the HTTP response header (jwt)

Issue a GET request to http://localhost:8080/jax-rs-with-jwt/resources/books and include the JWT in the HTTP Authorization header (prepend it with Bearer)

I am sure there are lots of other uses of JWT itself. Hopefully this gives a decent starting point to using them within your JAX-RS services

Cheers!