WordPress: Choose password at registration (Multisite)

pw-at-signup.php

<?php

//Plugin Name: Choose password at registration (Multisite)
//Description: Doesn't change the confirmation screen or email

add_action('signup_extra_fields', 'ask_for_password');
function ask_for_password( $errors ) {
	if ( $errmsg = $errors->get_error_message('bad_password') ) {
		echo '<p class="error">'.$errmsg.'</p>';
	}
	?>	<p>You can set your password here. If left blank, a random one will be generated for you.</p>
		<label>Password:</label><input type='password' name='password1' />
		<label>Password again:</label><input type='password' name='password2' />
	<?php
}

add_filter( 'wpmu_validate_user_signup', 'verify_password' );
function verify_password( $result ) {
	$password1 = $_POST['password1'];
	$password2 = $_POST['password2'];
	//don't require a password
	//if empty, let WP use generated password
// 	if ( empty( $password1 ) ) {
// 		$result['errors']->add('bad_password', 'Please provide a password');
// 	}
	if ( $password1 != $password2  ) {
		$result['errors']->add('bad_password', 'Passwords do not match');
	}
	if ( strlen( $password1 ) > 0 && strlen( $password1 ) < 8 ) {
		$result['errors']->add('bad_password', 'Password is too short');
	} 
	return $result;
}

add_filter( 'add_signup_meta', 'save_password_in_signup_meta' );
function save_password_in_signup_meta( $meta ) {
	$password1 = $_POST['password1'];
	$meta['password'] = $password1;
	return $meta;
}

add_action('wpmu_activate_user', 'apply_password_during_activation', 10, 3 );
function apply_password_during_activation( $user_id, $password, $meta ) {
	//if password was provided, use that
	if ( strlen( $meta['password'] ) > 0)
		wp_set_password( $meta['password'], $user_id );
}

wp 3.9.2 ,I put those code to theme functions.php & not work....
when debug,I found that the wp-signup.php file no use, because I delete it ,wp reister still work.
and the function show_user_form contain do_action( 'signup_extra_fields', $errors ); not called.

Thank you! Good input point for complex registrations on WP MS