Content Security Policy
Content Security Policy (CSP) is an added layer of security that helps to detect and mitigate certain types of attacks, including Cross-Site Scripting (XSS) and data injection attacks. These attacks are used for everything from data theft, to site defacement, to malware distribution.
To enable CSP, you need to configure your web server to return the Content-Security-Policy HTTP header. (Sometimes you may see mentions of the X-Content-Security-Policy header, but that's an older version and you don't need to specify it anymore.)
Alternatively, the <meta> element can be used to configure a policy, for example:
<meta
http-equiv="Content-Security-Policy"
content="default-src 'self'; img-src https://*; child-src 'none';" />
A policy is described using a series of policy directives, each of which describes the policy for a certain resource type or policy area. Your policy should include a default-src policy directive, which is a fallback for other resource types when they don't have policies of their own (for a complete list, see the description of the default-src directive). A policy needs to include a default-src or script-src directive to prevent inline scripts from running, as well as blocking the use of eval(). A policy needs to include a default-src or style-src directive to restrict inline styles from being applied from a <style> element or a style attribute. There are specific directives for a wide variety of types of items, so that each type can have its own policy, including fonts, frames, images, audio and video media, scripts, and workers.
'nonce-*'
A cryptographic nonce (only used once) to allow scripts. The server must generate a unique nonce value each time it transmits a policy. It is critical to provide a nonce that cannot be guessed as bypassing a resource's policy is otherwise trivial. This is used in conjunction with the script tag nonce attribute. For example, nonce-DhcnhD3khTMePgXwdayK9BsMqXjhguVV.
'sha*-*'
sha256, sha384, or sha512. Followed by a dash and then the sha* value. For example, sha256-jzgBGA4UWFFmpOBq0JpdsySukE1FrEN5bUpoK8Z29fY=.