We are required to disable all logins to DNN during any type upgrades to our DNN. We have a solution that is pretty ridiculous to disable logins but still allow our testers a backdoor to login, which basically means that if a user could figure it out they could login to during the maintenance period.
I would like to suggest a setting adding to the "Admin Settings" page called, "Disable Logins" which would turn off all logins to the site except for Host.
Then right below that setting an approved login list that users could be added to that could login during this period for testing other purposes.
Finally a message would need to be displayed during logins that the Login has been temporarily disabled.