Currently KerberosTicket methods are not thread safe and requires
external synchronization. External locking is mostly advantages if one
application/library is in control of all threads accessing the
resource, which is not likely to be the norm for KerberosTicket.
Multiple parties, including the login module, jgss module, and the
application can have threads accessing the ticket content, they need
to synchronize on the same lock. The usage pattern suggests internal
locking might be a better choice.