Vlad,
Our customer bought a ERP product named Aptify, it comes with with a web API they call EBusiness and they recommend using Sitefinity as CMS and provide modules you can use in your websites.
For EBusiness to work, the application pool running sitefinity needs to use a windows account assigned an Aptify client license since they use windows authentication.
I didn't go very far troubleshooting but as far as I can dig up EBusiness loads its own module in <httpModules> section. When we install Sitefinity 3.7 patch, the entire website breaks with null reference exceptions in the following EBusiness method call:
Unfortunately I don't have a way to trace the exact point in that method where is failing but what we see is the web server unable to authenticate to the database server, authentication is refused by the OS, not SQL. So it seems something in
CmsHttpModule is changing the way windows authentication is passed between servers.
We asked our customer to contact Aptify and report this issue. Maybe they can provide some help tracking this down.