add_shortcode( 'form_login_customers', 'login_customers' );
  function login_customers( $atts ) {
  if ( isset( $_POST['customer_loginBTN'] ) ) {
  $post_login = array(
        'post_pass' => $_POST['pass'],
        'post_user'   => $_POST['user']
  );
    $input_username= $post_login['post_user'];
    $input_password= md5($post_login['post_pass']);

    $blogusers = get_users( [ 'role__in' => [ 'sales', 'basic' ] ] );
    // Array of WP_User objects.
    foreach ( $blogusers as $user ) {
        $username= $user->user_login;
        $password= $user->user_pass;

        $user = array();
        $user['user_login'] = $input_username;
        $user['user_password'] = $input_password;
        $user['remember'] = true;
        $users = wp_signon( $user, false );
        if ( is_wp_error($users) )
            echo $users->get_error_message()."<br>";


    }

}
?>
<form method = "post" class="custom_login">
    <div class="form-group">
        <input type="text" name="user"  placeholder="Username" required="">
    </div>
    <div class="form-group">
        <input type="password" name="pass" placeholder="Password" required="">
    </div>
    <input type="submit" name="customer_loginBTN">
</form>
<?php
}