Implementing Content Security Policy in Phoenix LiveView

Dan Schultzer has written a blog post detailing the implementation of a Content Security Policy (CSP) header in a Phoenix LiveView application. The intent is to counter typical cross-site scripting (XSS) attacks. Dan notes that while using default CSP recommendations like "default-src 'self';" can mitigate many common security risks, there are cases where additional sources, such as images or Content Delivery Networks (CDN), need to be allowed. He discusses the challenges with inline styles and scripts, suggesting the use of nonces to allow for dynamic content in a secure manner within the constraints of the CSP. He then provides a detailed guide on setting up CSP with Phoenix LiveView, including creating a new module for CSP handling, similar to the CSRF plug in structure, and implementing it within the router pipeline. He finishes with considerations about security risks and demonstrates the module with unit tests.