Using the rkerberos gem to authenticate a user with a working Kerberos set up and store the credentials in the default file cache. Doesn't seem to add anything for my typical use case and, in fact, we lose some capability compared with k5start and the kstart package.
# Assumes a working krb5 setup with /etc/krb5.conf.
# Doesn't seeem to work without username and realm.
cc = Kerberos::Krb5::CredentialsCache.new('jslatter@JSLATTERY.ORG')
# /tmp/krb5cc_1000 now exists. klist just shows principals.
k = Kerberos::Krb5.new
k.get_init_creds_keytab('jslatter', 'krb5.keytab', nil, cc)
# klist shows creds.
cc.destroy
# /tmp/krb5cc_1000 is gone.