Question how is Protected Directories handled with nginx + apache?

[larryk]

OS ‪CentOS Linux 7.2.1511 (Core)‬
Product Plesk Onyx
Version 17.0.17 Update #18, last updated on Mar 7, 2017 03:24 AM

for this vhost:
"fpm application served by apache" is used

how does plesk control the passwords, access, user timeouts or related settings when it comes to
using Protected Directories?

where are the settings configured at?

my issue:
getting odd, random 401 errors on Apache SSL/TLS access FROM my client who obviously has authorization and has already logged in.

i'm trying to think WAY, way out of the box to come up with any idea how or why that could be happening.

thanks!
for any ideas, advice, etc.