Adventures in setting up NetBackup 8.0 VMware Web Client Plugin files

So I was working on deploying my NetBackup 8.0 into my home lab when it hit me:

"Hey! Why don't you go ahead and load the Web Client plugin for NetBackup into vCenter! Then you can see all your VMware backups right from there AND be able to run restores!" *Author's comments: If you want to skip the details and get to the answer skip down to the "problem and solution" section towards the bottom

"Good idea!" I thought to myself. Little did I realize this would lead me down the path of around 6hrs of digging through web pages and scratching my head.

My setup is as follows:
VMware VCSA 6.5, 2 PowerEdge 1950's, Synology 1815+ NAS, Windows 2016 DC+DNS Server, Windows 2016 Certificate Authority Server (setup for other reasons), Windows 2012 R2 NetBackup Server.

Followed Veritas' guide to setup the web plugin which says you need a web server (thought my Synology would have worked). Run the jar file as instructed in the guide:

Put in my vCenter name, username, password and click "Validate". It returns a message that the plugin is not installed currently and to please provide the URL to install the file.

Point it at the Synology (and later I installed IIS on my backup server and pointed it there) and clicked Register. It came back with a message that the registration was successful.

"Great! That was easy!" I thought to myself. So I log out of vCenter and log back in. No plugin. Go to Administration -> Client Plugins. Nothing there. Weird I thought. Go to event viewer and sure enough it says Plugin registration was successful. Meh, ok, vCenter just needs to be bounced. I log into the console and give it a quick "init 6" and give it space to do it's VMware magic.

Log back in. Nada. Ooookay. Now this is really getting unusual, since I ran the plugin installer again and it said everything was installed and good. So I open my vCenter page with the /mob path, go to "content", followed by "ExtensionManager". look around and it's there, happy as could be. I can pull up details. No errors, no nothing.

Tried removing and reinstalling the plugin, both via their tool to remove/reinstall, as well as remove using "ExtensionManager". Throw in a few reboots for good measure. Nope, not having it. Search for VCSA plugins missing, or plugin permissions. Nothing of substance. Search NetBackup plugin knowledge base. Zilch.

Went to Twitter to beg the all knowing Gurus for sage advice... Is that a cricket I hear?

Ok, so now that the drama has been setup, here's the problem and solution:
All documentation implies that you're good to use any web server to host the plugin installer file. Even the above mentioned picture shows "http or https". The documents don't tell you until page 81/82 of an 85 page document, in the troubleshooting section no less (which you don't see if you're following guides from their knowledge base instead of using the actual PDF listed above), that you that in order to register a plugin with VMware VCSA 6.5 you either MUST use a https enabled web server in order to register the plugin OR will have to edit a configuration file on the VCSA to tell it to trust http. This is an excerpt from the document:
NetBackup plug-in not shown in vSphere Web Client portal even after registration
If the plug-in is hosted on an HTTP site instead of an HTTPS site, you must make the vSphere Web Client trust the HTTP connections. If not, the connection does not download and deploy the plug-in. To build this trust, add the following directive to the file:

allowHttp = true

The file can be located in the following directories:
Windows: C:\ProgramData\VMware\vSphere Web Client\ 
Linux: /var/lib/vmware/vsphere-client


Solution: Setup an https web certificate on my IIS box and register again. Eureka! It worked!
Hope this helps someone. This issue could potentially effect other plugin registration besides NetBackup, so I wanted to share the answer. If your plugin is installed correctly and yet missing from vCenter, this may be your culprit.