How can I fix the Flask CSRF protect error 'The referrer does not match the host'?

What are the common causes of the 'The referrer does not match the host' error in Flask CSRF protection?

The "The referrer does not match the host" error in Flask CSRF protection typically occurs due to discrepancies between the host of the request and the referrer header. Here are some common causes and how to address them:

Common Causes Proxy Servers: If your application is behind a proxy server (like Nginx), the referrer header might be altered or stripped, causing the mismatch. Ensure that your proxy server is correctly configured to pass the referrer header.

SSL/TLS Configuration: If your application is served over HTTPS, but the referrer header is missing or incorrect, this can trigger the error. Verify that your SSL/TLS settings are correctly configured.

Incorrect Server Name: If the SERVER_NAME configuration in your Flask app does not match the actual server name, this can cause the error. Ensure that the SERVER_NAME is correctly set in your configuration.

Browser Compatibility: Some browsers might handle the referrer header differently, especially when using webkit-based browsers. Test your application in different browsers to see if the issue persists.