/*
 * call-seq:
 *   get_default_principal -> string
 *
 * Call krb5_cc_get_principal() to get the principal from the default cachefile.  Returns the default principal on success, raises Krb5Auth::Krb5::Exception on failure.
 */
static VALUE Krb5_get_default_principal(VALUE self)
{
  struct ruby_krb5 *kerb;
  char *princ_name;
  VALUE result;
  krb5_error_code krbret;
  krb5_ccache cc;

  Data_Get_Struct(self, struct ruby_krb5, kerb);
  if (!kerb) {
    NOSTRUCT_EXCEPT();
    return Qfalse;
  }

  krbret = krb5_cc_default(kerb->ctx, &cc);
  if (krbret) {
    Krb5_register_error(krbret);
    return Qfalse;
  }

  krbret = krb5_cc_get_principal(kerb->ctx, cc, &kerb->princ);
  if (krbret) {
    krb5_cc_close(kerb->ctx, cc);
    Krb5_register_error(krbret);    
    return Qnil;
  }

  krb5_cc_close(kerb->ctx, cc);

  krbret = krb5_unparse_name(kerb->ctx, kerb->princ, &princ_name);
  if (krbret) {
    Krb5_register_error(krbret);    
    return Qnil;
  }

  result = rb_str_new2(princ_name);

  free(princ_name);

  return result;
}