GitLab SSO with CAS

I have integrated CAS login on my instance. There is no problem when user clicks on Sign-in with CAS button it is redirected to CAS page and returns back to GitLab instance. But i want to make user auto logged in if user already logged in on CAS server. So user will not need to click sign-in button if he/she is already signed in on CAS. Is it possible to do that?