Book club: JSON Web Tokens

This month for our book club Daniel, Lars, Vince and I read Hardcoded secrets, unverified tokens, and other common JWT mistakes which wasn’t quite what we’d thought when it was picked. We had been expecting an analysis of JSON web tokens themselves as several us had been working in the area and had noticed various talk about problems with the standard but instead the article is more a discussion of the use of semgrep to find and fix common issues, using issues with JWT as examples.

We therefore started off with a bit of a discussion of JWT, concluding that the underlying specification was basically fine given the problem to be solved but that as with any security related technology there were plenty of potential pitfalls in implementation and that sadly many of the libraries implementing the specification make it far too easy to make mistakes such as those covered by the article through their interface design and defaults. For example interfaces that allow interchangable use of public keys and shared keys are error prone, as is is making it easy to access unauthenticated data from tokens without clearly flagging that it is unauthenticated. We agreed that the wide range of JWT implementations available and successfully interoperating with each other is a sign that JWT is getting something right in providing a specification that is clear and implementable.

Moving on to semgrep we were all very enthusiastic about the technology, language independent semantic matching with a good set of rules for a range of languages available. Those of us who work on the Linux kernel were familiar with semantic matching and patching as implemented by Coccinelle which has been used quite successfully for years to both avoiding bad patterns in code and making tree wide changes, as demonstrated by the article it is a powerful technique. We were impressed by the multi-language support and approachability of semgrep, with tools like their web editor seeming particularly helpful for people getting started with the tool, especially in conjunction with the wide range of examples available.

This was a good discussion (including the tangential discussions of quality problems we had all faced dealing with software over the years, depressing though those can be) and semgrep was a great tool to learn about, I know I’m going to be using it for some of my projects.