Implement Trusted Types

[henrym2]

Expected Behavior

Trusted types will help reduce the scope of browser XSS sinks in the application. However as the application is primarily server side, with limited scope of javascript interaction, the implementation of this feature should simply provide a mechanism for defining Trusted Types headers and, if possible, an implementation guide as to how to use them in an application

Steps to implement a solution

• Understand Symfony CSP scope
• Define headers for Trusted types
• Devise sensible Trusted types policies
• Produce trusted types policy implementation guides