Cannot Return Custom HTTP Error Details Remotely

This is a strange one. I'm running MVC 3 and have a custom action result that wraps exceptions and returns a message along with the standard HTTP error.

public class ExceptionResult : ActionResult
    private readonly Exception _exception;

    public ExceptionResult(Exception exception)
        _exception = exception;

    public override void ExecuteResult(ControllerContext context)
        var response = context.HttpContext.Response;
        response.ContentType = ContentType.Json;

        var baseEx = _exception as BaseException ?? new ServerException(_exception);

        var result = baseEx.GetResult();

        var json = result.ToJSON();
        response.StatusCode = (int)result.Status.Code;

When I run this locally I get exactly what I expect:

HTTP/1.1 400 Bad Request
Cache-Control: no-store
Content-Type: application/json; charset=utf-8
Server: Microsoft-IIS/7.5
X-AspNet-Version: 4.0.30319
Date: Thu, 01 Dec 2011 19:00:03 GMT
Content-Length: 81

{"error":"invalid_request","error_description":"Parameter grant_type is missing"}

But when I try to connect from a different machine I get the standard IIS error message instead:

HTTP/1.1 400 Bad Request
Cache-Control: no-store
Content-Type: text/html
Server: Microsoft-IIS/7.5
X-AspNet-Version: 4.0.30319
Date: Thu, 01 Dec 2011 19:02:33 GMT
Content-Length: 11

Bad Request


There must be some http module somewhere in the IIS pipeline that is swallowing the response and rewriting the content. I wrote a module to log the request and response and it's returning exactly what I expect however what actually makes it to the browser is wrong.

2011-12-02 15:39:00,518 - ======== Request ========
2011-12-02 15:39:00,518 - GET /oauth/2/token HTTP/1.1
2011-12-02 15:39:00,519 - Cache-Control: max-age=0
2011-12-02 15:39:00,519 - Connection: keep-alive
2011-12-02 15:39:00,519 - Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
2011-12-02 15:39:00,519 - Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.3
2011-12-02 15:39:00,519 - Accept-Encoding: gzip,deflate,sdch
2011-12-02 15:39:00,519 - Accept-Language: en-US,en;q=0.8
2011-12-02 15:39:00,519 - Host: micah-pc:8095
2011-12-02 15:39:00,519 - User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/535.2 (KHTML, like Gecko) Chrome/15.0.874.121 Safari/535.2
2011-12-02 15:39:00,519 - =========================
2011-12-02 15:39:00,519 - OAuth exception occurred.
BoomTown.OAuth.OAuthException: Parameter grant_type is missing
   at BoomTown.OAuth.Request.TokenRequest.GetRequestValidator() in C:\code\BoomTown\Api\BoomTown.OAuth\Request\TokenRequest.cs:line 19
   at BoomTown.OAuth.Request.OAuthRequestBase.Validate() in C:\code\BoomTown\Api\BoomTown.OAuth\Request\OAuthRequestBase.cs:line 33
   at BoomTown.OAuth.Request.OAuthRequestBase..ctor(HttpRequestBase request, IOAuthServiceLocator serviceLocator) in C:\code\BoomTown\Api\BoomTown.OAuth\Request\OAuthRequestBase.cs:line 28
   at BoomTown.OAuth.Request.TokenRequest..ctor(HttpRequestBase request, IOAuthServiceLocator serviceLocator) in C:\code\BoomTown\Api\BoomTown.OAuth\Request\TokenRequest.cs:line 13
   at BoomTown.Api.Web.Controllers.OAuth.V2.OAuthController.Token() in C:\code\BoomTown\Api\BoomTown.Api.Web\Controllers\OAuth\V2\OAuthController.cs:line 26
2011-12-02 15:39:00,520 - ======= Response =======
2011-12-02 15:39:00,520 - HTTP/1.1 400 Bad Request
2011-12-02 15:39:00,520 - Cache-Control: no-store
2011-12-02 15:39:00,520 - X-AspNet-Version: 4.0.30319
2011-12-02 15:39:00,520 - Content-Type: application/json; charset=utf-8
2011-12-02 15:39:00,520 - {"error":"invalid_request","error_description":"Parameter grant_type is missing"}


Thanks to a little sleuthing I was able to figure it out. I setup IIS tracing which confirmed my suspicions that it was related to the customerrormodule which was intercepting my requests and overwriting my error messages. I kept monkeying with the

  <customErrors />

settings but to no avail. I was on the right track, but since it's IIS 7 that I'm running I needed to change the correct web.config section like this:

    <httpErrors errorMode="Detailed" />

Now all my custom JSON messages come through perfectly. Big thanks to Jason Finneyfrock for the tag team on this one.


In your web.config, do you have httpErrors defined to only be DetailedLocalOnly? I'm not sure whether or not the content would be removed in this situation.

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