How to Fix the 'Origin is not allowed by Access-Control-Allow-Origin' Error?

Accessing Cross-Origin Resources: Addressing the "Origin is not allowed by Access-Control-Allow-Origin" Error

For applications that utilize Ajax requests to communicate with remote servers across different domains, the dreaded "Origin is not allowed by Access-Control-Allow-Origin" error is a common obstacle. It occurs when an application attempts to make requests to a different domain than the application's origin, and the server is not configured to allow cross-origin access.

Resolve the issue, we can modify the server response header to include the "Access-Control-Allow-Origin" parameter. This parameter specifies the domains or URIs that are allowed to make cross-origin requests to the server.

Setting the Response Header with PHP

For PHP, the response header can be set using the header() function, as shown below:

<?php header('Access-Control-Allow-Origin: *'); ?>

The asterisk (*) in the "Access-Control-Allow-Origin" header indicates that the server will allow requests from any origin. Alternatively, you can whitelist specific origins by replacing the asterisk with the desired domains, such as:

<?php header('Access-Control-Allow-Origin: http://example.com'); ?>

Caveat: Security Implications

It's important to note that allowing cross-origin access without specific origin whitelisting poses security risks. By using the wildcard "*", you are potentially exposing your application to cross-site scripting (XSS) and other attacks. Therefore, it's crucial to only allow access from trusted origins.

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