How to use package composer in controller (jasig\phpcas))

You are trying to access the phpCAS class in the context of the App\Controllers namespace.
That's why you're getting the error.

PHP Code:

// before class
use phpCas; 
// or use backslash
-> \phpCas::client() 


Thanks a lot !!
I think i've tried all the pattern but not only 'use phpCAS'... my bad.
It work's now.