Migrating WordPress intranet and adding SSL

Good day WordPress Pro’s

I am stuck, and i have done so much research and can not find the correct way.

Long story short, i created a localhost intranet as a side line project on my companies web server. They now decided they like it and want to use it as their new company Intranet.

I now need to move the site to a new folder, which is easy and i can do, but i also need to add SSL. (from http to https).

Now my issue is, because it is intranet, i can not get a certificate, and i need to have the site as HTTPS so that i can use it with office 365 API.

There is no way to access this site from outside our network.

So do i just change the configs to change the address to HTTPS? Will office 365 see the site as secure with no Certificate?

I do not know any more ??

The page I need help with: [log in to see the link]