ASP.NET Forms login fails in Windows Domain

Question

Hi,

I'm currently integrating a web application into a customers network. The application has been successfully used many times.

But here we've got the following problem: If the login page is requested just by the hostname everything works fine, but if the FQDN is used the login page just reloads withous doing anything. There's no error displayed.

http://hostname:port/Login.aspx => fine

http://hostname.intern.customer.domain.foo.com => doesn't work, no error (The FQDN is quite long)

The login page is very simple:

<asp:Login ID="loginCtrl" runat="server">
    <LabelStyle HorizontalAlign="Left" />
</asp:Login>

Codebehind:

 protected override void OnLoad(EventArgs e)
 {
    if (!this.IsPostBack)
    {
        FormsAuthentication.SignOut();
        Context.User = null;
    }
    base.OnLoad(e);
 }

Any recommendations?

NOTE: The problem cannot be reproduced by adding the FQDN to hosts file on my local computer.

EDIT:

The application is hosted by a cassini derivate.

The MembershipProvider uses a WCF service on the same machine.

EDIT:

Part of web.config:

<authentication mode="Forms">
  <forms loginUrl="Login.aspx"/>
</authentication>
<authorization>
  <deny users="?"/>
</authorization>
<membership defaultProvider="my">
  <providers>
    <clear/>
    <add name="my" type="MyMembershipProvider"/>
  </providers>
</membership>

Answer 1

I'm guessing the application needs to be installed on different app servers? If so the problem is with the configuration of IIs (or whatever server is hosting the application.)

A nice overview of forms authentication is located here. I would take a look at the configuration sections since they can change from machine to machine. ms forms overview