ASP.NET forms authentication doesn't work with reverse proxy

I have an ASP.NET application. As well as local users accessing the application directly, I want to expose it to external users through a reverse proxy (which is running on a different machine in the DMZ)

for example, say internal users use the URL http://intranet1/myApplication/default.aspx, external users might use the URL http://www.mycompany.com/externalApplication/default.aspx

this is quite simple to set up with URL rerwiting, but there is a problem when forms authentication is turned on. if an external user hits the URL site, forms auth tries to automatically send them to the login page which redirects them to the relative url /myApplication/LoginPage.aspx. as far as the web app is concerned, t开发者_Go百科he application root is at /myApplication not /externalApplication. Of course the external user coming in through the firewall does not understand this URL so the request fails with a 404

is there a sensible solution for this?

You should not redirect to "/myApplication/LoginPage.aspx" but to "~/Login.aspx", so it would be correctly mapped depends on which URL is user hits on.

<authentication mode="Forms">
  <forms loginUrl="~/Login.aspx" timeout="2880" />
</authentication>