function wp_authenticate_username_password($user, $username, $password) {
if ( is_a($user, \'WP_User\') ) { return $user; }

if ( empty($username) || empty($password) ) {
    $error = new WP_Error();

    if ( empty($username) )
        $error->add(\'empty_username\', __(\'<strong>ERROR</strong>: The username field is empty.\'));

    if ( empty($password) )
        $error->add(\'empty_password\', __(\'<strong>ERROR</strong>: The password field is empty.\'));

    return $error;
}

$userdata = get_user_by(\'login\', $username);

if ( !$userdata )
    return new WP_Error(\'invalid_username\', sprintf(__(\'<strong>ERROR</strong>: Invalid username. <a href="%s" title="Password Lost and Found">Lost your password</a>?\'), wp_lostpassword_url()));

if ( is_multisite() ) {
    // Is user marked as spam?
    if ( 1 == $userdata->spam)
        return new WP_Error(\'invalid_username\', __(\'<strong>ERROR</strong>: Your account has been marked as a spammer.\'));

    // Is a user\'s blog marked as spam?
    if ( !is_super_admin( $userdata->ID ) && isset($userdata->primary_blog) ) {
        $details = get_blog_details( $userdata->primary_blog );
        if ( is_object( $details ) && $details->spam == 1 )
            return new WP_Error(\'blog_suspended\', __(\'Site Suspended.\'));
    }
}

$userdata = apply_filters(\'wp_authenticate_user\', $userdata, $password);
if ( is_wp_error($userdata) )
    return $userdata;

if ( !wp_check_password($password, $userdata->user_pass, $userdata->ID) )
    return new WP_Error( \'incorrect_password\', sprintf( __( \'<strong>ERROR</strong>: The password you entered for the username <strong>%1$s</strong> is incorrect. <a href="%2$s" title="Password Lost and Found">Lost your password</a>?\' ),
    $username, wp_lostpassword_url() ) );

$user =  new WP_User($userdata->ID);
return $user;
}

这是我在wordpress中找到的代码。但我在里面冲浪，但我无法找到在哪里检索数据库的用户名或密码。我只想知道wordpress使用什么查询来检索密码和用户名。