Request header not in Access-Control-Allow-Headers list

Question

In my API, I have the following code:

public class CustomOAuthProvider : OAuthAuthorizationServerProvider
{

    public override Task MatchEndpoint(OAuthMatchEndpointContext context)
    {
        if (context.OwinContext.Request.Method == "OPTIONS" && context.IsTokenEndpoint)
        {
            context.OwinContext.Response.Headers.Add("Access-Control-Allow-Methods", new[] { "POST" });
            context.OwinContext.Response.Headers.Add("Access-Control-Allow-Headers", 
                new[] { 
                    "access-control-allow-origin", 
                    "accept", 
                    "x-api-applicationid", 
                    "content-type", 
                    "authorization" 
                });
            context.OwinContext.Response.Headers.Add("Access-Control-Allow-Origin", new[] { "*" });
            context.OwinContext.Response.StatusCode = (int)HttpStatusCode.OK;

            context.RequestCompleted();

            return Task.FromResult<object>(null);
        }

        return base.MatchEndpoint(context);
    }

    // ... even more code, but not relevant

}

When I connect to this API from Chrome, everything works fine. When I connect from the same computer to the same API, but only from another Internet Explorer 11 browser, I get the following error:

SEC7123: The request header x-api-applicationid was not present in the Access-Control-Allow-Headers List.

I debugged the code and I see that the headers are being added to the response. Even IE shows headers:

What expects IE?

Update

If I reordered the headers from

new[] { 
    "access-control-allow-origin", 
    "accept", 
    "x-api-applicationid", 
    "content-type", 
    "authorization" 
}

at

new[] { 
    "content-type",
    "accept",
    "access-control-allow-origin",
    "x-api-applicationid", 
    "authorization" 
}

The error message changes to:

SEC7123: The request header access-control-allow-origin was not in the Access-Control-Allow-Headers List.

Thus, it always throws an error in the third header.

Answer 1

, .

//Startup.cs
public void ConfigureOAuth(IAppBuilder app)
{
    app.Use(async (context, next) =>
    {
        IOwinRequest req = context.Request;
        IOwinResponse res = context.Response;
        if (req.Path.StartsWithSegments(new PathString("/oauth2/token")))
        {
            var origin = req.Headers.Get("Origin");
            if (!string.IsNullOrEmpty(origin))
            {
                res.Headers.Set("Access-Control-Allow-Origin", origin);
            }
            if (req.Method == "OPTIONS")
            {
                res.StatusCode = 200;
                res.Headers.AppendCommaSeparatedValues("Access-Control-Allow-Methods", "GET", "POST");
                res.Headers.AppendCommaSeparatedValues("Access-Control-Allow-Headers", "authorization", "content-type", "x-api-applicationid", "access-control-allow-origin");
                return;
            }
        }
        await next();
    });

    // rest of owin Oauth config
}

MatchEndpoint CustomOAuthProvider.cs

Answer 2

, , AJAX. OPTIONS application/x-www-form-urlencoded, ,

content-type: application/x-www-form-urlencoded

application/x-www-form-urlencoded

contentType.

:

$.ajax({
    url: 'http://www.example.com/api/Account/Token',
    contentType: 'content-type: application/x-www-form-urlencoded',
    method: 'POST',
    data: {
        grant_type: "password",
        username: $('#username').val(),
        password: $('#password').val()
    },
});

RIGHT:

$.ajax({
    url: 'http://www.example.com/api/Account/Token',
    contentType: 'application/x-www-form-urlencoded',
    method: 'POST',
    data: {
        grant_type: "password",
        username: $('#username').val(),
        password: $('#password').val()
    },
});

Answer 3

No need to remove MatchEndPoint

Instead of adding an array element, simply add the value Comma-Separated as the element of the first array in Access-Control-Allow-Headers

Instead

 context.OwinContext.Response.Headers.Add("Access-Control-Allow-Headers", 
                new[] { 
                    "access-control-allow-origin", 
                    "accept", 
                    "x-api-applicationid", 
                    "content-type", 
                    "authorization" 
                });

using

context.OwinContext.Response.Headers.Add("Access-Control-Allow-Headers", 
    new[] { 
        "access-control-allow-origin,accept,x-api-applicationid,content-type,authorization" 
    });