Unable to Navigate to external domain (auth endpoint) in MS Dynamics CRM 2013/2015 IFD

The standard practice for my company when deploying web servers is to use a host header, which probably made sense at some point but it surely made for an interesting Friday.

I'm tired, so I will just present the facts: If you are configuring IFD and can't get to the external domain endpoint, the problem might be that you have a host header for your https binding.

The external domain endpoint is normally: https://auth.adomain.com/FederationMetadata/2007-06/FederationMetadata.xml and is the last step on the configure IFD wizard.

Ensure that IIS is configured without a host header for the https binding: