Cross-site AJAX requests are requests made by JavaScript code running on one domain (or origin) to a server hosted on a different domain (or origin). Due to security concerns, modern web browsers block such requests by default, because it is a way for malicious websites to make unauthorized requests to other websites on behalf of unsuspecting users.

To allow cross-site AJAX requests, the server hosting the other domain must explicitly allow it. This is done using the Cross-Origin Resource Sharing (CORS) mechanism.

CORS involves the server sending additional HTTP headers in the response to the client’s request that indicate whether the request is allowed and which origins are allowed to make the request. If the client’s domain is not allowed, the browser will prevent the response from being processed by the client-side JavaScript code.

To allow cross-site AJAX requests, the server should include the Access-Control-Allow-Origin header in the response. For example, if you want to allow requests from any origin, you can use the following header:

Access-Control-Allow-Origin: *

This will allow requests from any domain to access the server’s resources.

If you want to allow requests only from specific domains, you can specify those domains instead of using the wildcard. For example:

Access-Control-Allow-Origin: https://example.com

This will allow requests only from the https://example.com domain.

It’s important to note that allowing cross-site AJAX requests can pose security risks, so it’s important to use it judiciously and only when necessary. You should also ensure that the server-side code properly validates and sanitizes all incoming requests to prevent unauthorized access to sensitive data.