Content security policies
The Content Security Policy (CSP) is a set of directives that inform the user's browser of locations from which an application is allowed to load resources. These locations are provided in the form of URL schemes, including the use of an asterisk (*) to represent all URLs. Each directive governs a specific resource type that affects what is displayed in a browser. Collectively, the directives are sent to the client in the Content-Security-Policy HTTP header. Each browser type and version obey as much of the policy as they can. If a browser does not understand a directive, it is ignored; otherwise it is explicitly followed.