Magento 2 – Check if it is Frontend or Backend

Since no one came up with a good reason not to do what I was asking I assume that my method is kind of safe. So, in order not to leave this question open, I decided to add the code as an answer and mark it as accepted.
So I have a new extension called Easylife_Simulate with the following files: app/etc/modules/Easylife_Simulte.xml - the declaration file:

<?xml version="1.0"?>
<config>
    <modules>
        <Easylife_Simulate>
            <codePool>local</codePool>
            <active>true</active>
            <depends>
                <Mage_Customer />
            </depends>
        </Easylife_Simulate>
    </modules>
</config>

app/code/local/Easylife/Simulte/etc/config.xml - the configuration file

<?xml version="1.0"?>
<config>
    <modules>
        <Easylife_Simulate>
            <version>0.0.1</version>
        </Easylife_Simulate>
    </modules>
    <global>
        <helpers>
            <easylife_simulate>
                <class>Easylife_Simulate_Helper</class>
            </easylife_simulate>
        </helpers>
        <models>
            <easylife_simulate>
                <class>Easylife_Simulate_Model</class>
            </easylife_simulate>
        </models>
        <resources>
            <easylife_simulate_setup>
                <setup>
                    <module>Easylife_Simulate</module>
                    <class>Mage_Customer_Model_Resource_Setup</class>
                </setup>
            </easylife_simulate_setup>
        </resources>
    </global>
    <frontend>
        <routers>
            <easylife_simulate>
                <use>standard</use>
                <args>
                    <module>Easylife_Simulate</module>
                    <frontName>simulate</frontName>
                </args>
            </easylife_simulate>
        </routers>
    </frontend>
    <adminhtml>
        <events>
            <controller_action_layout_render_before_adminhtml_customer_edit>
                <observers>
                    <easylife_simulate>
                        <class>easylife_simulate/observer</class>
                        <method>addAutoLoginButton</method>
                    </easylife_simulate>
                </observers>
            </controller_action_layout_render_before_adminhtml_customer_edit>
        </events>
    </adminhtml>
    <admin>
        <routers>
            <adminhtml>
                <args>
                    <modules>
                        <Easylife_Simulate before="Mage_Adminhtml">Easylife_Simulate_Adminhtml</Easylife_Simulate>
                    </modules>
                </args>
            </adminhtml>
        </routers>
    </admin>
</config>

app/code/local/Easylife/Simulate/sql/easylife_simulate_setup/install-0.0.1.php - install script - adds a new customer attribute:

<?php
$this->addAttribute('customer', 'login_key', array(
    'type'      => 'text',
    'label'     => 'Auto login key',
    'input'     => 'text',
    'position'  => 999,
    'required'  => false
));

app/code/local/Easylife/Simulate/Model/Observer.php - observer to add a button in the customer admin edit form

<?php
class Easylife_Simulate_Model_Observer extends Mage_ProductAlert_Model_Observer{
    public function addAutoLoginButton($observer){
        $block = Mage::app()->getLayout()->getBlock('customer_edit');
        if ($block){
            $customer = Mage::registry('current_customer');
            $block->addButton('login', array(
                'label'     => Mage::helper('customer')->__('Login as this customer'),
                'onclick'   => 'window.open(\''.Mage::helper('adminhtml')->getUrl('adminhtml/simulate/login', array('id'=>$customer->getId())).'\')',
            ), 100);
        }

    }
}

app/code/local/Easylife/Simulate/controllers/Adminhtml/SimulateController.php - the admin controller that handles the click on the button generated above.

<?php
class Easylife_Simulate_Adminhtml_SimulateController extends Mage_Adminhtml_Controller_Action{
    public function loginAction(){
        $id = $this->getRequest()->getParam('id');
        $customer = Mage::getModel('customer/customer')->load($id);
        if (!$customer->getId()){
            Mage::getSingleton('adminhtml/session')->addError(Mage::helper('easylife_simulate')->__('Customer does not exist'));
            $this->_redirectReferer();
        }
        else {
            $key = Mage::helper('core')->uniqHash();
            $customer->setLoginKey($key)->save();
            $this->_redirect('simulate/index/index', array('id'=>$customer->getId(), 'login_key'=>$key));
        }
    }
}

app/code/local/Easylife/Simulate/controllers/IndexController.php - the frontend controller that makes the autologin.

<?php
class Easylife_Simulate_IndexController extends Mage_Core_Controller_Front_Action{
    public function indexAction(){
        $id = $this->getRequest()->getParam('id');
        $key = $this->getRequest()->getParam('login_key');
        if (empty($key)){
            $this->_redirect('');
        }
        else{
            $customer = Mage::getModel('customer/customer')->load($id);
            if ($customer->getId() && $customer->getLoginKey() == $key){
                $customer->setLoginKey('')->save();
                Mage::getSingleton('customer/session')->setCustomerAsLoggedIn($customer);
                Mage::getSingleton('customer/session')->renewSession();
            }
            $this->_redirect('customer/account/index');
        }
    }
}

app/code/local/Easylife/Simulte/Helper/Data.php - the module helper

<?php
class Easylife_Simulate_Helper_Data extends Mage_Core_Helper_Abstract{

}

That's it. It seams to work for me. Like I said in the question, the downside is that if 2 admins press the login button for the same customer at (approximately) the same time, one of them will not be logged in. But he can repeat the process a few seconds later.

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What have you don recently? Any changes on the site?