You should be able to login using your username and password to the Mobile apps, as well as to the Web service.
If you are facing any issues please send us a screenshots of the error to email@example.com
Thanks Dana. We require 2 factor auth to 365 which includes certificate auth. THe iOS app says to select a cert to login, but it hangs at that point. It does not list the cert.
My cert is installed on the iphone. Other apps like Cisco Jabber prompt for the cert. I will send to the support email suggeted too.