OK - consider this as it is how you have your own website setup.
I go to submit a support ticket in the helpdesk, try to logon - and keep getting user or password invalid. I try this 1 million times as I know its correct.
Suddenly it dawns on me try try and login into BILLING (whmcs) instead. I can then submit a ticket.
Why cant users login to Vision directly when using the login share?!
Yes your users can directly login to vision client portal with whmcs login details provided they should not register their emails with vision first.