enable Single Sign On (SSO) for ALM12.53 using SiteMinder

we would like to enable SSO for ALM12.53 using SiteMinder, our current situation is:

we use local login ID to ALM at this moment, all those local login ID does NOT exist in our Activive Directory, but all those ID has proper company email address attached.

all the active directory (AD) IDs do NOT exist in ALM either.

if we turn on SSO, login to my workstation using AD ID, will i be able to login to ALM automatically? or  we have to create all AD IDs in ALM and assign IDs to projects in order for SSO to work? this would be a huge work for us.

any suggestion would be appreciated.

thx

Jen