k5_kt_get_principal
ret = k5_kt_get_principal(k5->ctx, keytab, &k5->me);
krb5_error_code k5_kt_get_principal(krb5_context context, krb5_keytab keytab,
code = k5_kt_get_principal(context, cred->client_keytab, &princ);
code = k5_kt_get_principal(context, cred->keytab, &princ);