PHP Strict-Origin-When-Cross-Origin

As a developer, you may have encountered Cross-Origin Resource Sharing (CORS) issues when working with APIs or making HTTP requests from a domain that is different from the one hosting the server. The PHP strict-origin-when-cross-origin header is a tool that can help prevent CORS vulnerabilities.

What is CORS?

CORS is a security mechanism that prevents a web page from making AJAX requests to a different domain than the one that served the original web page. By default, web browsers respect this requirement to ensure that malicious code cannot access sensitive data or perform unauthorized actions on behalf of users.

However, there are legitimate use cases for making cross-origin requests, such as accessing public APIs or loading resources from a CDN. In such cases, the HTTP response from the server must include the appropriate CORS headers to indicate that cross-origin requests are allowed.

What is strict-origin-when-cross-origin?

The strict-origin-when-cross-origin header is a relaxation of the Same-Origin Policy that allows requests from a different origin if the request is only changing the scheme (http/https) or the port number. This means that if you are accessing an endpoint on the same server, but from a different domain or subdomain, the request will be allowed.

However, if the request is trying to access a different server altogether, such as a third-party API, the browser will still block the request unless the server explicitly allows it by returning the appropriate CORS headers.

How to implement strict-origin-when-cross-origin in PHP

To include the strict-origin-when-cross-origin header in a PHP script, you can simply use the header() function. Here's an example:

header('Cross-Origin-Embedder-Policy: require-corp');
header('Cross-Origin-Opener-Policy: same-origin');
header('Cross-Origin-Resource-Policy: same-origin-allow-popups');
header('Cross-Origin-Resource-Policy: same-site');
header('Referrer-Policy: strict-origin-when-cross-origin');

In this example, we are not only setting the strict-origin-when-cross-origin header, but also several other policies that help enforce secure behaviors, such as requiring same-origin embedding and opening policies.

Conclusion

The strict-origin-when-cross-origin header is a powerful tool for ensuring secure cross-origin requests while still allowing legitimate use cases. As a developer, it's important to understand how CORS works and how to implement the appropriate headers to avoid security vulnerabilities.