Why Does My AngularJS POST Request Fail with a 404 for the Preflight Request?

AngularJS POST Request Failure: HTTP 404 for Preflight Request

In AngularJS, an unresolved "XMLHttpRequest cannot load" error can occur during POST requests. This is caused by an invalid HTTP status code (404) for the preflight request that precedes the actual POST. The preflight request is intended to check if the requested operation is permitted, ensuring compliance with Cross-Origin Resource Sharing (CORS) policies.

Root Cause: Missing CORS Headers

The underlying cause of the error lies in the server's failure to properly handle the preflight OPTIONS request. To enable cross-origin requests, the server must set appropriate CORS headers.

Solution: Adding CORS Headers Server-Side

In SlimPHP, you can add CORS headers to the response object:

<code class="php">$app->response()->headers->set('Access-Control-Allow-Headers', 'Content-Type');
$app->response()->headers->set('Content-Type', 'application/json');
$app->response()->headers->set('Access-Control-Allow-Methods', 'GET, POST, OPTIONS');
$app->response()->headers->set('Access-Control-Allow-Origin', '*');</code>

Solution: Disabling Preflight Requests Client-Side

Alternatively, you can disable preflight requests client-side by resetting the common headers in AngularJS:

<code class="js">app.config(function ($httpProvider) {
  $httpProvider.defaults.headers.common = {};
  $httpProvider.defaults.headers.post = {};
  $httpProvider.defaults.headers.put = {};
  $httpProvider.defaults.headers.patch = {};
});</code>

Additional Considerations

For POST requests involving sensitive data, you may need to implement authentication and authorization mechanisms, such as JSON Web Tokens (JWT), to secure the connection. It's essential to thoroughly understand CORS and ensure proper handling of OPTIONS requests to prevent security breaches.

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