We have a Kerberos setting to remove realm part from the user
principal name (`remove_realm_name`). If this is true then
the realm name is removed to form username but in the process,
the realm name is lost. For scenarios like Kerberos cross-realm
authentication, one could make use of the realm name to determine
role mapping for users coming from different realms.
This commit adds user metadata for `realm` and `user_principal_name`.