Verifique el nombre de usuario correcto en el formulario de inicio de sesión personalizado

He usado el tutorial de Jeff Star para crear mi propio formulario de inicio de sesión personalizado http://digwp.com/2010/12/login-register-password-code/ . Funciona muy bien, pero tengo un problema. En el formulario de restablecimiento de contraseña, si alguien ingresa su nombre de usuario de manera incorrecta (para que no se verifique), se lo expulsará al wp-login.php? Action = lostpassword predeterminado con el mensaje de error.

¿Hay alguna manera de redirigir a mi propia página de error?

¡Gracias!

El código que publicó en ese tutorial (muy bonito, por cierto) publica el formulario en el módulo incorporado "restablecer contraseña" que redirige al login.php por error, pero puede cambiar eso y construir el suyo basado en el original y agregar a la página de plantilla, cambie:

<form method="post" action="<?php echo site_url('wp-login.php?action=lostpassword', 'login_post') ?>" class="wp-user-form">
    <div class="username">
        <label for="user_login" class="hide"><?php _e('Username or Email'); ?>: </label>
        <input type="text" name="user_login" value="" size="20" id="user_login" tabindex="1001" />
    </div>
    <div class="login_fields">
        <?php do_action('login_form', 'resetpass'); ?>
        <input type="submit" name="user-submit" value="<?php _e('Reset my password'); ?>" class="user-submit" tabindex="1002" />
        <?php $reset = $_GET['reset']; if($reset == true) { echo '<p>A message will be sent to your email address.</p>'; } ?>
        <input type="hidden" name="redirect_to" value="<?php echo $_SERVER['REQUEST_URI']; ?>?reset=true" />
        <input type="hidden" name="user-cookie" value="1" />
    </div>
</form>

a:

<form method="post" action="<?php echo $_SERVER['REQUEST_URI']; ?>" class="wp-user-form">
<div class="username">
    <label for="user_login" class="hide"><?php _e('Username or Email'); ?>: </label>
    <input type="text" name="user_login" value="" size="20" id="user_login" tabindex="1001" />
</div>
<div class="login_fields">
    <?php do_action('login_form', 'resetpass'); ?>
    <input type="submit" name="user-submit" value="<?php _e('Reset my password'); ?>" class="user-submit" tabindex="1002" />

    <?php
    if (isset($_POST['reset_pass']))
    {
        global $wpdb;
        $username = trim($_POST['user_login']);
        $user_exists = false;
        if (username_exists($username))
        {
            $user_exists = true;
            $user_data = get_userdatabylogin($username);
        } elseif (email_exists($username))
        {

            $user_exists = true;
            $user = get_user_by_email($username);
        } else
        {
            $error[] = '<p>' . __('Username or Email was not found, try again!') . '</p>';
        }
        if ($user_exists)
        {
            $user_login = $user->user_login;
            $user_email = $user->user_email;
            // Generate something random for a password... md5'ing current time with a rand salt
            $key = substr(md5(uniqid(microtime())), 0, 8);
            // Now insert the new pass md5'd into the db
            $wpdb->query("UPDATE $wpdb->users SET user_activation_key = '$key' WHERE user_login = '$user_login'");
            //create email message
            $message = __('Someone has asked to reset the password for the following site and username.') . "\r\n\r\n";
            $message .= get_option('siteurl') . "\r\n\r\n";
            $message .= sprintf(__('Username: %s'), $user_login) . "\r\n\r\n";
            $message .= __('To reset your password visit the following address, otherwise just ignore this email and nothing will happen.') . "\r\n\r\n";
            $message .= get_option('siteurl') . "/wp-login.php?action=rp&key=$key\r\n";
            //send email meassage
            if (FALSE == wp_mail($user_email, sprintf(__('[%s] Password Reset'), get_option('blogname')), $message))
            $error[] = '<p>' . __('The e-mail could not be sent.') . "<br />\n" . __('Possible reason: your host may have disabled the mail() function...') . '</p>';
        }
        if (count($error) > 0)
        {
            foreach ($error as $e)
            {
                echo $e . '<br/>';
            }
        } else
        {
            echo '<p>' . __('A message will be sent to your email address.') . '</p>';
        }
    }
    ?> 
    <input type="hidden" name="reset_pass" value="1" />
    <input type="hidden" name="user-cookie" value="1" />
</div>
</form>

Aquí hay una versión actualizada del código de @bainternet con los errores de sintaxis corregidos, la sugerencia de @Val y el generador de claves de wp-login.php 3.4.2:

global $wpdb;
$username = trim($_POST['user_login']);
$user_exists = false;
// First check by username
if ( username_exists( $username ) ){
    $user_exists = true;
    $user = get_user_by('login', $username);
}
// Then, by e-mail address
elseif( email_exists($username) ){
        $user_exists = true;
        $user = get_user_by_email($username);
}else{
    $error[] = '<p>'.__('Username or Email was not found, try again!').'</p>';
}
if ($user_exists){
    $user_login = $user->user_login;
    $user_email = $user->user_email;

    $key = $wpdb->get_var($wpdb->prepare("SELECT user_activation_key FROM $wpdb->users WHERE user_login = %s", $user_login));
    if ( empty($key) ) {
        // Generate something random for a key...
        $key = wp_generate_password(20, false);
        do_action('retrieve_password_key', $user_login, $key);
        // Now insert the new md5 key into the db
        $wpdb->update($wpdb->users, array('user_activation_key' => $key), array('user_login' => $user_login));
    }

    //create email message
    $message = __('Someone has asked to reset the password for the following site and username.') . "\r\n\r\n";
    $message .= get_option('siteurl') . "\r\n\r\n";
    $message .= sprintf(__('Username: %s'), $user_login) . "\r\n\r\n";
    $message .= __('To reset your password visit the following address, otherwise just ignore this email and nothing will happen.') . "\r\n\r\n";
    $message .= network_site_url("wp-login.php?action=rp&key=$key&login=" . rawurlencode($user_login), 'login') . "&redirect_to=".urlencode(get_option('siteurl'))."\r\n";
    //send email meassage
    if (FALSE == wp_mail($user_email, sprintf(__('[%s] Password Reset'), get_option('blogname')), $message))
    $error[] = '<p>' . __('The e-mail could not be sent.') . "<br />\n" . __('Possible reason: your host may have disabled the mail() function...') . '</p>';
}
if (count($error) > 0 ){
    foreach($error as $e){
                echo $e . "<br/>";
            }
}else{
    echo '<p>'.__('A message will be sent to your email address.').'</p>'; 
}

Todavía tenía problemas con la tecla de restablecimiento que no funcionaba correctamente, el enlace en el correo electrónico me redirigía a la página de restablecimiento de contraseña estándar con el parámetro URL que indica un problema con la clave, por lo que seguí más de cerca el archivo wp-login.php e incluyó el objeto $ wp_hasher, esto solucionó el problema y el restablecimiento de contraseña en el correo electrónico ahora funciona

if (($_SERVER['REQUEST_METHOD'] === (string) 'POST') && (isset($_POST['reset_pass']))) {

// Acccess global properties
global $wpdb, $wp_hasher;


// Variables
$error_pass_reset = array();
$username         = (string) trim($_POST['user_login']);
$user_exists      = (bool)   false;



// ---- USERNAME OR EMAIL EXISTS ---- //
if (username_exists($username)) {
    $user_exists = (bool)   true;
    $user        = (object) get_user_by('login', $username);
} // end if

else if (email_exists($username)) {
    $user_exists = (bool)   true;
    $user        = (object) get_user_by('email', $username);
} // end else if

else {
    $error_pass_reset[] = '<p>Username or Email was not found, please try again.</p>';
} // end else



// ---- USER EXISTS ---- //
if ($user_exists === (bool) true) {
    // Variables
    $user_login = (string) $user -> user_login;
    $user_email = (string) $user -> user_email;


    // Generate password reset key
if (empty($key)) {
    $key = (string) wp_generate_password(20, false);

    do_action('retrieve_password_key', $user_login, $key);


    // Create the $wp_hasher object
    if (empty($wp_hasher)) {
        require_once(ABSPATH . WPINC . '/class-phpass.php');

        $wp_hasher = new PasswordHash(8, true);
    }

    // Reset key with hasher applied (MD5 has string output)
    $hashed = (string) time() . ':' . $wp_hasher -> HashPassword($key);


    // Insert the new key into the database
    $wpdb -> update(
        $wpdb -> users,
        array(
            'user_activation_key' => $hashed
        ),
        array(
            'user_login' => $user_login
        )
    );
} // end if


    // Email message
    $message = (string)
    'Someone requested that the password be reset for the following account:' . "\r\n\r\n" .

    get_option('siteurl') . "\r\n\r\n" .

    'Username: ' . $user_login . "\r\n\r\n" .
    'If this was a mistake, just ignore this email and nothing will happen.' . "\r\n\r\n" .
    'To reset your password, visit the following address:' . "\r\n\r\n" .

    get_option('siteurl') . '/wp-login.php?action=rp&key=' . $key . '&login=' . $user_login . "\r\n";


    // Send email
    if ((bool) false === wp_mail($user_email, get_option('blogname') . ' Password Reset', $message)) {
        $error_pass_reset[] = '<p>The e-mail could not be sent at this time.</p>' . "\n";
    } // end if
} // end if


// Send the rest password email
do_action('login_form', 'resetpass');

} // end if (($_SERVER['REQUEST_METHOD'] === (string) 'POST') && (isset($_POST['reset_pass'])))