503 Error when accessing feeds from nuget.exe or Visual Studio

When I attempt to access my ProGet feeds through Visual Studio or nuget.exe it errors out with a 503 error.
I am using:

LDAP authentication
Integrated Authentication
IIS Hosted
With custom AppPool identity which has access to my database and filesystem

Product: ProGet
Version: 3.5.5

What version of NuGet are you using?

Also- did this used to work, or is this the first time you are trying it?

I'm using nuget 2.8. Come to think of it hasn't worked. I had to manually upload packages previously and I never tried adding ProGet as a package source.

The interesting thing is I tried installing to a different machine and I get the same problem.

Strange. Well, an HTTP 503 pretty much has to be coming from IIS rather than ProGet itself, as we don't explicitly return that error code at all. It might be useful to record a Fiddler trace to see what URLs NuGet is trying to connect to, and to see if the server returns any more information that isn't being displayed.

I also tried going the non-IIS route and I was getting the same behavior.

So upon doing a fiddler trace and seeing nothing coming through when I used nuget.exe against our internal repo, I tried it against nuget.org and lo and behold that failed too.
It turns out for prior things I had HTTP_PROXY and HTTPS_PROXY environment variables set and nuget.exe didn't like it. This carried over to Visual Studio as well. After removing those variables everything started working again.

So, sorry this wasn't ProGet at all (thankfully).