Http Request not reaching the IIS module

Question

During development of an IIS module for basic authentication, I stocked to a problem. The module is working fine when browsing the pages, but when calling web-services it seems that request does not reach the module and some in-the-middle module takes control of request.

using fiddler, I found out when Content-type in http request header is set to application/json that in the middle module/handler is triggered. so following request does not work:

when working fine, the server should ask client to send the user credentials by setting the WWW-Authenticate header in response

GET /WebServices/service.asmx/someMethod?param=test HTTP/1.1
Host: localhost
Connection: keep-alive
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.22 (KHTML, like Gecko) Chrome/25.0.1364.152 Safari/537.22
Accept-Encoding: gzip,deflate,sdch
Accept-Language: en-US,en;q=0.8
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.3
Content-Type: application/json

asdfasdf
asdfasdfasdf

response: notice the jsonerror header in response

HTTP/1.1 401 Unauthorized
Content-Type: application/json; charset=utf-8
Server: Microsoft-IIS/7.5
jsonerror: true
X-Powered-By: ASP.NET
Date: Mon, 11 Mar 2013 23:49:02 GMT
Content-Length: 105

{"Message":"Authentication failed.","StackTrace":null,"ExceptionType":"System.In
validOperationException"}

where this one works fine: notice that there is no content-type

GET /WebServices/service.asmx/someMethod?param=test HTTP/1.1
Host: localhost
Connection: keep-alive
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.22 (KHTML, like Gecko) Chrome/25.0.1364.152 Safari/537.22
Accept-Encoding: gzip,deflate,sdch
Accept-Language: en-US,en;q=0.8
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.3

asdfasdf
asdfasdfasdf

and the correct response is: notice the WWW-Authenticate header in response

HTTP/1.1 401 Unauthorized
Location: http://localhost/WebServices/service.asmx/someMethod?param=test
Server: Microsoft-IIS/7.5
WWW-Authenticate: Basic
X-Powered-By: ASP.NET
Date: Mon, 11 Mar 2013 23:59:48 GMT
Content-Length: 0

Answer 1

Well, that in-the-middle module was ScriptModule where we had both 3.5 and 4.0 version being added in the config. inspecting them through dotpeek, I found that the script module checks request's content-type against being application/json and then tries to handle the request as a REST request or webservice call.

By removing them, nothing special happened. I assume that they are to be used when script manager or Microsoft Specific AJAX services are used. You can find more about it in ASP.Net Ajax Programming Tricks