Module Login as customer in Prestashop 1.6, 1.7

With this module, as an admin you are now able to login as a customer in order to make orders, payments and edits to his profile. Source code included, open source.

The module consists in 2 files: the main module file Fc_LoginAsCustomer and the front controller file Fc_LoginAsCustomerLoginModuleFrontController.

Step 1. Create the main module

Create the main module file in /modules/fc_loginascustomer/fc_loginascustomer.php:

<?php
if (!defined("_PS_VERSION_")) {
  exit();
}

class Fc_LoginAsCustomer extends Module
{
  public function __construct()
  {
    $this->name = "fc_loginascustomer";
    $this->tab = "back_office_features";
    $this->version = "1.0.0";
    $this->author = "Myros";
    $this->controllers = ["login"];

    $this->bootstrap = true;
    parent::__construct();

    $this->displayName = $this->l("FC Login as customer");
    $this->description = $this->l("Allows you login as customer");

    $this->ps_versions_compliancy = ["min" => "1.6", "max" => _PS_VERSION_];
  }

  public function install()
  {
    return parent::install() && $this->registerHook("displayAdminCustomers");
  }

  public function hookDisplayAdminCustomers($params)
  {
    $customer = new CustomerCore((int) Tools::getValue("id_customer"));
    $link = $this->context->link->getModuleLink($this->name, "login", [
      "id_customer" => $customer->id,
      "xtoken" => $this->makeToken($customer->id),
    ]);
    if (!Validate::isLoadedObject($customer)) {
      return;
    }
    return '<div class="panel">
              <div class="panel-heading">
                <i class="icon-file"></i> ' .
      $this->l("FC Login As Customer") .
      " v" .
      $this->version .
      '
              </div>
              <p class="text-center">
                <a class="btn btn-default" href="' .
      $link .
      '" target="_blank">
                  <i class="icon-user"></i> ' .
      $this->l("Login as customer") .
      " " .
      $customer->email .
      '
                </a>
              </p>
          </div>';
  }

  public function makeToken($id_customer)
  {
    return md5(_COOKIE_KEY_ . $id_customer . date("Ymd"));
  }
}

Step 2. The Front Controller

and the Front controller in /modules/fc_loginascustomer/controllers/front/login.php:

<?php

class Fc_LoginAsCustomerLoginModuleFrontController extends ModuleFrontControllerCore
{
  public $ssl = true;

  public function postProcess()
  {
    parent::postProcess();
    $id_customer = (int) Tools::getValue("id_customer");
    if (!$id_customer || $id_customer < 0) {
      die('bad $id_customer');
    }
    $xTokenOk = Tools::getValue("xtoken") == $this->module->makeToken($id_customer);
    if (!$xTokenOk) {
      die("bad xtoken");
    }
    $customer = new Customer($id_customer);
    if (!Validate::isLoadedObject($customer)) {
      die("bad customer object");
    }
    $customer->logged = 1;
    $this->context->customer = $customer;
    $this->context->cookie->id_customer = $customer->id;
    $this->context->cookie->customer_lastname = $customer->lastname;
    $this->context->cookie->customer_firstname = $customer->firstname;
    $this->context->cookie->logged = 1;
    $this->context->cookie->check_cgv = 1;
    $this->context->cookie->is_guest = $customer->isGuest();
    $this->context->cookie->passwd = $customer->passwd;
    $this->context->cookie->email = $customer->email;
    Tools::redirect("index.php?controller=my-account");
  }
}

Source https://www.prestashop.com/forums/topic/444031-free-module-login-as-customer/ refactored, cleaned and simplified.