python - Flask JWT extend validity of token on each request

Question

Scenario

A logged in user will have a token expiry of 24 hours. Within that period, all request with @jwt_required decorator will have the current access token's expiry extended by another 24 hours. There is a maximum validity of 168(24 * 7) hours.

It is possible to use access_token and refresh_token.

ret = {
        'access_token': create_access_token(identity=username, fresh=True),
        'refresh_token': create_refresh_token(identity=username)
    }

But that means every API call from my applicatino will be two requests: 1. Actual HTTP Request 2. Refresh the auth token

@app.route('/refresh', methods=['POST'])
@jwt_refresh_token_required
def refresh():
    current_user = get_jwt_identity()
    ret = {
        'access_token': create_access_token(identity=current_user)
    }
    return jsonify(ret), 200

Is there a way to implicitly extend an auth token?

Answer 1

Author of flask-jwt-extended here. Technically you cannot actually extend a token, you can only replace it with a new JWT that has a new expires time. There are a few ways you could simulate this though.

First, instead of having the client request a new token, you could have the server itself just implicitly send back a new token on every request. You could send the new JWTs back in a header instead of in the JSON payload, so that you wouldn't have to modify you JSON data to account for the possibility of a new JWT. Your clients would need to be aware of this though, they would need to check for that new header on every request and replace their current JWT with the new one if it is present. You could probably use a flask after_request method to do this, so you didn't have to add that functionality to all your endpoints. A similar effect could be achieved when storing the JWTs in cookies, with the differences being that cookies are automatically stored in your browser (so your client wouldn't have to manually look for them on every request), and with the added complexity of CSRF protection if you go this route (http://flask-jwt-extended.readthedocs.io/en/latest/tokens_in_cookies.html).

The above should work fine, but you will be creating a lot of access tokens that are thrown away right after being created, which probably isn't ideal. A variation of the above is to check if the token is near expiring (maybe if it is more then half way to being expired) and only create and return a new token if that is the case. Another variation of this would be to have the client check if the token is about to expire (via javascript) and if it is, use the refresh token to request a new access token. To do that, you would need to split the JWT on dots ('.'), base64 decode the second set of strings from that split (index 1), and grab the 'exp' data from there.

A second way you could do this is actually wait for a token to expire, and then use the refresh token to generate a new access token and remake the request (reactive instead of proactive). That might look like making a request, checking if the http code is 401, if so use the refresh token to generate a new access token, then making the request again.

Hope this helps :)