I slightly updated ShowContexts.aspx recently during some IIS7 research work. So I thought I post the new version here.
Features:
- shows authentication and impersonation settings
- shows configured role and membership providers
- shows configured trust level (well – for completeness only – you need full trust for this page to work correctly)
- shows the IPrincipal/IIdentity types on Context.User and Thread.CurrentPrincipal
- shows the name and authentication type on Context.User and Thread.CurrentPrincipal
- shows the thread identity (when impersonation is enabled)
- shows the IIS LogonUser identity (used by FileAuthorizationModule)
- shows the client cert (and some embedded information like the UPN if available)
- shows roles (for Windows-, Roles and GenericPrincipal)
- allows to save an aggregated config.web (with all settings from machine.config down to the vdir)
- can set a FormsAuthentication ticket to simulate authentication
HTH
leastprivilege.com 
The download link is not working. Also the link to the tool from IIS.NET is also broken.
Do you have an up-to-date link ? Thanks.
see here: https://leastprivilege.com/archive/