When non-admin user trying to login using login.do eg : <instance_name>.service-now.com/login.do.
Users are observing "Security constraint prevent access to requested page"
It does not mean the user is unable to login, the user has logged in. However, due to ACL on login_redirect user is experiencing "Security constraint prevent access to requested page"
ACL : "login_redirect" - https://<instance_name>.service-now.com/nav_to.do?uri=sys_security_acl.do?sys_id=cbfb0ca3931102009c8579b4f47ffbc2
Above mentioned ACL is responsible for the security constraint issue, it need snc_internal and snc_external role for the login redirection.
Non-Admin user trying to login has role "snc_internal", after adding "snc_external" role, user is able to see the page.