A WordPress auto-login php script. Upload this file anywhere in your website, and simply login by visiting the file from your browser. For example, if you upload this file in your ROOT, visit "http://your-domain.com/auto-login.php" to automatically login to your WordPress dashboard.

auto-login.php

<?php

require_once('wp-load.php');
$loginusername = 'admin'; //Replace your username for which user you want to login.
$user = get_user_by( 'login', $loginusername );
$user_id = $user->ID;
wp_set_current_user( $user_id, $loginusername );
wp_set_auth_cookie( $user_id );
do_action( 'wp_login', $loginusername, $user );
wp_redirect( admin_url() );
unlink(__FILE__);

?>

Alternate solution:

<?php
require_once( 'wp-load.php' );

$username = 'admin';

if ( !($user_to_login = get_user_by( 'login', $username )) ) {
	if ( !( $user_to_login = get_user_by( 'email', $username )) ) {
	   $admin_users   = get_users( array( 'role' => 'administrator' ) );
       $user_to_login = is_array( $admin_users ) && isset( $admin_users[0] ) ? $admin_users[0] : false;
    }
}

if ( $user_to_login instanceof WP_User ) {
	wp_set_current_user( $user_to_login->ID, $user_to_login->user_login );
	wp_set_auth_cookie( $user_to_login->ID );
	do_action( 'wp_login', $user_to_login->user_login, $user_to_login );
}

unlink( __FILE__ );
wp_redirect( admin_url() );


?>