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I have an ASP.NET form (a login page), when I POST the values to the server (windows, IIS 6), the request passes through a proxy and the POST pareameters end up getting lost and ultimately the page just refreshes as there are no POST parameters.

The thing is that this is not a constant issue as sometimes you can log in fine and generally if you clear your browser temp files it then works ok.

I ran Fiddler to check what's going on and basically I'm getting:

  • A regular POST request containing session id, POST data etc. The response (HTTP 407) contains a Proxy-Authenticate: Negotiate and Proxy-Support: Session-Based-Authentication header.

  • The next request to the server contains a Proxy-Authorization: Negotiate header containing a long string (base64 i think). This request does NOT contain the POST values. The response is another 407 and actually now that i look at it Fiddler displays 'HTTP/1.1 407 Proxy Authentication Required ( Access is denied. )' as the header.

  • Then there's a third request that contains the Proxy-Authorization header and returns 200 OK, but of course the POST values weren't sent Subsequent requests result in a HTTP/1.1 407 Proxy Authentication Required ( The ISA Server requires authorization to fulfill the request. Access to the Web Proxy filter is denied. ) response followed by a second successful but empty request.

The client won't let me bypass the proxy as it's intermittent and all other pages in the application (that include plenty of web forms) work fine.

Any ideas on what I can try?

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migrated from serverfault.com Jan 23 '12 at 18:30

This question came from our site for professional system and network administrators.

1 Answer

If you think it's the proxy, get the proxy admin to look at the logs for some of the failed requests, and compare them with a working request.

It's possible the proxy's been configured to look for certain content and when it finds it, it dumps it.

You mentioned that doing something on the client fixed it though (clearing cache files), so that implies it might not be the proxy directly, but something about the client configuration (possibly in concert with the proxy).

The Fiddler problem you've described sounds like a pure client-side problem. If it's (one user) on (one computer) in (one environment) that has the problem, it's probably just that client. If the client isn't sending the form values when it posts after Proxy authentication, that's basically a client bug - it should send those form values. Running an IE Reset Settings operation might help with that (also, looking at all the add-ins, etc, and trying it in No Addons mode).

Between the proxy logs, the client capture (Fiddler's probably fine for initial troubleshooting, but keep in mind it's not a completely transparent proxy and if Fiddler becomes part of the problem or modifies the request, it's Wireshark/Netmon time) and the target web server, there should be some evidence that something's wrong somewhere.

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