Add sudoers option to perform authentication even in non-interative mode.

If noninteractive_auth is set, authentication methods that do not
require input from the user's terminal may proceed.  It is off by
default, which restores the pre-1.9.9 behavior of "sudo -n".

plugins/sudoers/check.c

@@ -125,6 +125,12 @@ check_user_interactive(int validated, int mode, struct getpass_closure *closure)
 	FALLTHROUGH;
 
     default:
+	if (ISSET(mode, MODE_NONINTERACTIVE) && !def_noninteractive_auth) {
+	    validated |= FLAG_NO_USER_INPUT;
+	    log_auth_failure(validated, 0);
+	    goto done;
+	}
+
 	/* XXX - should not lecture if askpass helper is being used. */
 	lectured = display_lecture(closure->tstat);