android - Sign in activity to main activity -

i have main activity buttons on leads other activities have decided authenticate user make them sign in before can start using app. how go sign in activity main activity? use intent main activity?

in project , used in mainactivity:

    if (!sessionmanager.getinstance().hassignin())         startactivity(new intent(mainactivity.this, signinactivity.class)); 

and after this, user can still finish signinactivity , , mainactivity , if don't want users go mainactivity before sign in ,you need make sure signinactivity has override onkeydown event