I have just developed my first version of a module called Kernel::System::CustomerAuth::JoomlaSSO
It allows Joomla logged users to access directly OTRS Customer interface (with automatic login) with no need to type user and pw again. OTRS Customer Backend should be the same as joomla for it to work.
Some customizetion are need on Joomla and OTRS side, so it’s not a module yet.
If you are interested on it, contact me please.