I finally figured it out...
The culprit was java.exe sitting there and listening on port 443 thus not letting the website to bind to it. And there was an extra step to take in order to let it know which portal to go to...
So here are all the steps to get yer portal up and secure ;)
The website with all the portals, preffarably, has to be on a separate (dedicated) IP (though it might not be the case after I learned about SSL headers, but since I changed it to a dedicated IP I chose to leave it that way)
1. Go to IIS Manager
--- Click on the server name under Connections (on the left side)
--- Open "Server Certificates" in the middle section under IIS
--- Click on "Create Certificate Request..." on the right side under Actions
--- Fill it out and generate the Cert Request file that you give to CA
2. Buy a certificate
3. Go to IIS manager, again, and under Actions on the right side click on "Complete Certificate Request..."
--- You need to put the certificate text that you get from a CA into a text file with a .cer extention
4. Now go to the site (under sites)
--- once there, click "Bindings..." under Actions
--- add https with "All Unassigned" and select the SSL certificate
5. Now go to Start > Run... > cmd > enter (this way it should start cmd in Admin mode)
--- type
cd C:\Windows\System32\Inetsrv\
--- enter
--- then type
appcmd set site /site.name:"<IIS Site Name>" /+bindings.[protocol='https',bindingInformation='*:443:<host Header>']
--- Replace <IIS Site Name> with the name the site has in the IIS Manager, and <host Header> with the host header for that site (secure.domain.com)
--- enter
6. Go back to IIS Manager, restart the site (just in case)
7. Go to DNN portal that needs to be secured and enable SSL under Admin > Site Settings
Well the rest of the SSL options are up to you, depends on how you want to configure the site.
I hope my write up would help someone, I wish I found anything similar, would've saved me alot of time, but there is always someone who has to write it up, so might as well be me ;)
Cheers,
Val