Sure, it tells you that there's a header missing, but from where is it missing, and what should it be? Searching for it on the internet is likely to bring up a popular forum where the most common answer is worse than wrong – it's dangerous. This error is up there as one of the least helpful error messages. Since this sends a request with null origin, a full, proper implementation that would later allow to verify a fix, would require hosting this on a non-localhost HTTP server with a valid API key.How to Fix 'No 'Access-Control-Allow-Origin' Header Present' Chrome, press F12 to view the error in the console. tRequestHeader('Authorization',`Basic $`) Request.addEventListener('load', onLoad) Replacing with a valid API key isn’t required, the error occurs for any kind of response, not just 2xx. Just save this as index.html and run it in your browser. Thanks for the quick replies! While I cannot share our codebase, below is a snippet that reproduces the issue just as well, using bare bones JavaScript.

For example, Access-Control-Allow-Origin:, would allow JavaScript hosted at to read the response to the subsequent GET request.

There is a possible solution to this - if, instead, you were sending the requester Origin’s header contents back in the OPTIONS Access-Control-Allow-Origin header, that would make it possible for JavaScript to read your responses. Your server’s response is the following: HTTP/1.1 204 No ContentĪccess-Control-Allow-Headers: origin,content-type,content-length,user-agent,host,accept,authorizationĪccess-Control-Allow-Methods: OPTIONS,GETĪccess-Control-Expose-Headers: Location,www-authenticate,cache-control,pragma,content-type,expires,last-modifiedĬache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0Īs noted in my first post, Access-Control-Allow-Origin: * causes Chrome to block the response to the GET request from being read with the error I pasted there. Host: .ukĪccess-Control-Request-Headers: authorization rogue JavaScript’s request cannot fake being from a different origin. Note that I don’t control the headers sent in the OPTIONS request. It is unavoidable when an HTTP request with a header other than the four safe headers is sent by JavaScript, in this case Authorization.īelow is the OPTIONS request generated by the browser before my GET with Autorization: Basic header is sent. Unfortunately, I cannot avoid making an OPTIONS request, as that is a CORS preflight request automatically sent by the browser. Just for clarity, the authentication I’m using works, I am able to get the requested resource using curl. For Chrome to allow the application to read the response from the GET request, the OPTIONS request has to specify my origin in the ‘Access-Control-Allow-Origin’ header, not just the wildcard.ĭoes setting JavaScript domains for a key takes a long time (more than several hours) to start working? Do I need to do anything else to change the wildcard '*' ‘Access-Control-Allow-Origin’ header on OPTIONS request except setting the JavaScript domains entries for my REST API key? My API key has a JavaScript domain value provided that exactly matches the one I’m trying to get the response from and still, the header is a wildcard.

This makes this issue different from the topics I could find, where that header was missing. The credentials mode of requests initiated by the XMLHttpRequest is controlled by the withCredentials attribute.Īs you can see from the error and as I can see from the F12 Network tab, the ‘Access-Control-Allow-Origin’ in the preflight OPTIONS request is a wildcard ‘*’. 91), then hides the response from me due to CORS policy, with the following error:Īccess to XMLHttpRequest at '' from origin ' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: The value of the 'Access-Control-Allow-Origin' header in the response must not be the wildcard '*' when the request's credentials mode is 'include'. I need to set withCredentials to true so that the Authorization header is sent across different origins. I’m trying to use the basic REST API from a JavaScript application.

My issue is different from the topics found using search, the header is present, but has an invalid value.

I do understand how CORS works and what it’s supposed to guard against.

I searched and looked through probably all topics related to CORS at this point.

Before I get directed to use the search feature:

Access control allow origin fetch