iOS 10 Enterprise Deployment Failing - Authentication Required

Question

I have been working to solve this issue for about a month now and I'm finally turning to the good people of Stack Overflow for some assistance.

To make a long story short, our enterprise app provisioning profile expired, so I created a new profile, recompiled the app, and put the IPA and manifest.plist on our server. The issue is that the app refuses to actually download now. After the user clicks "Install" in the dialog on our website, they are bombarded with "Authentication Required" alerts, and no matter what is done, the app WILL NOT install. Per Apple's suggestion, I installed the IPA through Configurator 2 and it installs perfectly, so according to the documentation, this means the issue is not in the signing of the app. I have triple-checked to make sure everything in the manifest is 100% accurate, and the link to the manifest matches the example given in Apple's documentation. It fails in iOS 9 and iOS 10. It fails on my iPhone and iPad. IIS has the mime types setup correctly, and the server can ping Apple's servers required for Enterprise installations. I am no closer to solving this than I was a month ago. Has anybody had any issues with something similar to this? Any input at all will help tremendously. Thanks!