CORS error :Request header field Authorization is not allowed by Access-Control-Allow-Headers in preflight response

Problem

I am trying to send the request from one localhost port to the another. I am using angularjs on the frontend and node on the backend.

Since it is CORS request, In node.js, i am using

res.header('Access-Control-Allow-Origin', '*');
res.header('Access-Control-Allow-Methods', 'GET, POST, PUT, DELETE, PATCH');
res.header('Access-Control-Allow-Headers', 'Origin, X-Requested-With, Content-Type, Accept, Authorization');

and in the angular.js service file, I am using

return {
    getValues: $resource(endpoint + '/admin/getvalues', null, {
        'get': {
             method: 'GET',
             headers:{'Authorization':'Bearer'+' '+ $localStorage.token}
             }
     }),
}

I am getting the following error

Request header field Authorization is not allowed by Access-Control-Allow-Headers in preflight response.

Please help!

Problem courtesy of: Abhishek Kulshrestha

Solution

You have to add options also in allowed headers. browser sends a preflite request before original request is sent. see below

 res.header('Access-Control-Allow-Methods', 'GET,PUT,POST,DELETE,PATCH,OPTIONS');

From source https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/OPTIONS

In CORS, a preflight request with the OPTIONS method is sent, so that the server can respond whether it is acceptable to send the request with these parameters. The Access-Control-Request-Method header notifies the server as part of a preflight request that when the actual request is sent, it will be sent with a POST request method. The Access-Control-Request-Headers header notifies the server that when the actual request is sent, it will be sent with a X-PINGOTHER and Content-Type custom headers. The server now has an opportunity to determine whether it wishes to accept a request under these circumstances.

EDITED

You can avoid this manual configuration by using npmjs.com/package/cors npm package.I have used this method also, it is clear and easy.

Solution courtesy of: vikas

Discussion

This is an API issue, you won't get this error if using Postman/Fielder to send HTTP requests to API. In case of browsers, for security purpose, they always send OPTIONS request/preflight to API before sending the actual requests (GET/POST/PUT/DELETE). Therefore, in case, the request method is OPTION, not only you need to add "Authorization" into "Access-Control-Allow-Headers", but you need to add "OPTIONS" into "Access-Control-allow-methods" as well. This was how I fixed:

if (context.Request.Method == "OPTIONS")
        {
            context.Response.Headers.Add("Access-Control-Allow-Origin", new[] { (string)context.Request.Headers["Origin"] });
            context.Response.Headers.Add("Access-Control-Allow-Headers", new[] { "Origin, X-Requested-With, Content-Type, Accept, Authorization" });
            context.Response.Headers.Add("Access-Control-Allow-Methods", new[] { "GET, POST, PUT, DELETE, OPTIONS" });
            context.Response.Headers.Add("Access-Control-Allow-Credentials", new[] { "true" });

        }
Discussion courtesy of: Hung Vu

If you don't want to install the cors library and instead want to fix your original code, the other step you are missing is that Access-Control-Allow-Origin:* is wrong. When passing Authentication tokens (e.g. JWT) then you must explicitly state every url that is calling your server. You can't use "*" when doing authentication tokens.

Discussion courtesy of: user441058

This recipe can be found in it's original form on Stack Over Flow.