/*
 * call-seq:
 *   krb5.get_init_creds_password(user, password)
 *
 * Authenticates the credentials of +user+ using +password+, and has the effect
 * of setting the principal and context internally. This method must typically
 * be called before using other methods.
 */
static VALUE rkrb5_get_init_creds_passwd(VALUE self, VALUE v_user, VALUE v_pass){