As I have mentioned before, manager and operator users are able to use Web GUI. Local users created this way (see below) - are not.
aaa authentication local-user "webwebweb" group "Level-15"
Radius authenticated users can access Web GUI also, but failback to local user authentication is not working (except for manager and operator users).
aaa authentication web login radius server-group "RADIUS" local
aaa authentication web enable radius server-group "RADIUS" local
or
aaa authentication web login local
aaa authentication web enable local