[15] redirect to signin/login page instead of 403 Forbidden when signin required

[hisaltesse]

Impacted versions:
15
Steps to reproduce:
Go a any page restricted to signed in users
Current behavior:
A user who is not signed in get redirected to 403: Forbidden
Expected behavior:
A user who is no signed in should be redirected to the signin page
(Admin should have the option to enable redirection to signin page when a page requires to be signed in.)