Content Security Policy (CSP) is a security feature implemented by web browsers that allows you to specify which resources are allowed to be loaded on your website. CSP helps prevent web security attacks such as Cross-Site Scripting (XSS), Cross-Site Request Forgery (CSRF), and Clickjacking by preventing attackers from injecting malicious code or resources into a website.

CSP works by defining a whitelist of allowed sources for various types of content, such as scripts, stylesheets, images, fonts, and other resources. When a user visits your website, the browser checks whether each resource being loaded complies with the defined CSP policy. If a resource does not comply, the browser blocks it from loading and displays an error message to the user.

Here's an example of how to implement CSP:

const policy = 'default-src 'self' https://example.com; 
script-src 'self' https://example.com;
style-src 'self' https://example.com; font-src 'self' https://example.com; 
img-src 'self' data:;';

const element = document.createElement('meta');
element.name = 'Content-Security-Policy';
element.content = policy;
document.head.appendChild(element);

In this example, we are setting the `Content-Security-Policy` header to allow resources from the `self` origin (i.e., the same domain as the website) and the `https://example.com` origin. We also specify allowed sources for scripts, stylesheets, fonts, and images.

By defining a CSP policy, you can prevent attackers from injecting malicious code or resources into your website. For example, if an attacker tries to inject a script into your website that is not allowed by the CSP policy, the browser will block it from loading and display an error message to the user. This helps prevent attacks such as XSS, where an attacker tries to inject malicious code into a website and steal user data or perform unauthorized actions on their behalf.

Overall, Content Security Policy is a powerful tool for preventing web security attacks by allowing you to specify which resources are allowed to be loaded on your website. By implementing CSP, you can help protect your website and user data from malicious attacks.