Continuing the series of hardening embedded Tomcat in Java to meet Nessus security scans, I am back with an example of adding a Content Security Policy to your app. There are some ways in a more standard Tomcat server to provide CSP policies, but with an embedded server that can be more difficult.
I have used an embedded Tomcat server for years to build applications. The following example is using Tomcat 10, but the principle is the same or Tomcat 9. The main difference as a Tomcat 9 to 10 transition is moving from the javax namespace to jakarta. With more and more libraries, such as Jooq, moving to more modern Java versions; as well as, some of the new Java versions offering good performance improvements out of the box, it may be time for everyone to move to the Jakarta namespace. (Even if that means leaving some libraries such as Google OAuth behind)
In my recent example project going over how to use Pac4J for Oauth with Tomcat 10, I have added an example here of what the FilterBase class would look like. You then need to initialize the filter where you are starting the Tomcat thread. That will add the needed header to all the web requests your application processes.