How to properly handle a JWT refresh?

Question

I have an android app. It connects with a REST API developed with Jersey. My REST End points are secured with Tokens. Below is how I generate them.

Algorithm algorithm = Algorithm.HMAC256(secret);
String token = JWT.create()
    .withClaim("userName","myusername)
    .withExpiresAt(expirationDate)
    .sign(algorithm);

Below is how I validate the token

public boolean validateTokenHMAC256(String token, String secret) throws UnsupportedEncodingException, JWTVerificationException
    {       
        Algorithm algorithm = Algorithm.HMAC256(secret);


        JWTVerifier verifier = JWT.require(algorithm) 
                .build(); //Reusable verifier instance
            DecodedJWT jwt = verifier.verify(token);

            Claim usernameClaim = jwt.getClaim("username");
            String username = usernameClaim.asString();
            System.out.println(username);


        return true;
    }

In my REST API I have a filter and that filter checks every request to see whether the token is as it is. Below is the code.

@Secured
@Provider
@Priority(Priorities.AUTHENTICATION)
public class AuthenticationFilter implements ContainerRequestFilter{

    //private static String authorizationSecret = "ZXW24xGr9Dqf9sq5Dp8ZAn5nSnuZwux2QxdvcH3wQGqYteJ5yMTw5T8DBUJPbySR";

    public AuthenticationFilter()
    {
        System.out.println("test printing");
    }

    @Override
    public void filter(ContainerRequestContext crc) throws IOException
    {
        String headerString = crc.getHeaderString("Bearer");
        System.out.println("bluh: "+headerString);
        System.out.println("test printing");

        try
        {
            boolean validateToken = validateToken(headerString, AuthKey.authorizationSecret);
            System.out.println("valid");
        }
        catch(Exception e)
        {
            System.out.println("invalid");
            crc.abortWith(
                Response.status(Response.Status.UNAUTHORIZED).build());
        }

    }

    private boolean validateToken(String strToken, String secret) throws UnsupportedEncodingException, JWTVerificationException
    {
        Token token = new Token();
        return token.validateTokenHMAC256(strToken,secret);
    }



}

The above code will be called when the user login to the application. However the token will be expired in 60 minutes. I know that after the token is expired either I have to take the user back to sign in screen or refresh the token. I went through the advices in here and here

But I do not understand the following.

1. How can I figure out whether the token has to be renewed? I thought I should do that after it is expired, but seems that is not the case. If I ask it to refresh in now<exp it will refresh in every request.

2. How can I assign and send this token back to the user? Currently when the user login on, he will get the token and he will save it in a variable. For the refreshed token to work, do I have to call the login method again (So the token will be sent to the user) or JWT it self will handle the case?

3. How do I actually refersh using java-jwt ?

Answer 1

1. How can I figure out whether the token has to be renewed? I thought I should do that after it is expired, but seems that is not the case. If I ask it to refresh in now

You need to refresh the token before it is expired. Decide your policy:

• issue a fresh token in every request

• issue a fresh token when the current one is close to expire. e.g. 10 min

• let client app request a new token when it needs it using a "refresh service" of your api. For example

---

@GET
@Path("/jwt/refresh")
@Produces(MediaType.TEXT_HTML)
public String refresh(){
    //Build a returns a fresh JWT to client 
}

2. How can I assign and send this token back to the user?

If you issue a fresh token during a request, you can return it in a special header that client will read during processing of the response. If you publish a "refresh" service as described above, then the client will call it independently when the current JWT is close to expire

Redirect to login method is not a good alternative because you will lose the current request

3. How do I actually refresh using java-jwt

Just issue a new token