This is tested with 5.0.d and at this time latest versions of Android and iOS mobile clients. I've verified that the iOS client can login when sso is disabled. The iOS client fails in "Authenticate" in the diagnostics screen"
It's possible it's related to a CAS authentication issue we've seen on iOS due to cookies being suppressed at the SDK level. I don't remember if Kerberos SSO relies on cookies for authentication or not, but suspect it would.
This is fixed in v2.2 which is approaching the end of development and should be released in November.