Default Realm in kerberos-identity-provider is not used

The Default Realm property in kerberos-identity-provider is never read or used. The KerberosIdentityProvider implementation should make use of that property in the following prioritized way:

• A realm-qualified principal will not be modified before authentication
• A principal shortname will have Default Realm appended to it when it is not blank before authentication
• A principal shortname will not be modified if Default Realm is blank, and the underlying kerberos implementation will append the default_realm configured in krb5.conf