Provide a method to directly authenticate on Drupal 8.

- Fixes #186

spec/Drupal/Driver/Cores/Drupal8Spec.php

@@ -4,6 +4,7 @@
 
 use Drupal\Component\Utility\Random;
 
+use Drupal\Driver\Cores\CoreAuthenticationInterface;
 use PhpSpec\ObjectBehavior;
 use Prophecy\Argument;
 
@@ -23,4 +24,9 @@ function it_should_return_a_random_generator()
     {
         $this->getRandom()->shouldBeAnInstanceOf('Drupal\Component\Utility\Random');
     }
+
+    function it_is_an_auth_core()
+    {
+        $this->shouldBeAnInstanceOf(CoreAuthenticationInterface::class);
+    }
 }

src/Drupal/Driver/AuthenticationDriverInterface.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace Drupal\Driver;
+
+/**
+ * Indicates the driver can log users in and out on the backend.
+ */
+interface AuthenticationDriverInterface {
+
+  /**
+   * Logs the user in.
+   */
+  public function login(\stdClass $user);
+
+  /**
+   * Logs the user out.
+   */
+  public function logout();
+
+}

src/Drupal/Driver/Cores/CoreAuthenticationInterface.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace Drupal\Driver\Cores;
+
+/**
+ * The core has the ability to directly authenticate users.
+ */
+interface CoreAuthenticationInterface {
+
+  /**
+   * Logs a user in.
+   */
+  public function login(\stdClass $user);
+
+  /**
+   * Logs a user out.
+   */
+  public function logout();
+
+}

src/Drupal/Driver/Cores/Drupal8.php

@@ -13,12 +13,13 @@
 use Drupal\Core\Entity\ContentEntityInterface;
 use Drupal\taxonomy\Entity\Term;
 use Drupal\taxonomy\TermInterface;
+use Drupal\user\Entity\User;
 use Symfony\Component\HttpFoundation\Request;
 
 /**
  * Drupal 8 core.
  */
-class Drupal8 extends AbstractCore {
+class Drupal8 extends AbstractCore implements CoreAuthenticationInterface {
 
   /**
    * Tracks original configuration values.
@@ -612,4 +613,26 @@ protected function stopCollectingMailSystemMail() {
     }
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function login(\stdClass $user) {
+    $account = User::load($user->uid);
+    \Drupal::service('account_switcher')->switchTo($account);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function logout() {
+    try {
+      while (TRUE) {
+        \Drupal::service('account_switcher')->switchBack();
+      }
+    }
+    catch (\RuntimeException $e) {
+      // No more users are logged in.
+    }
+  }
+
 }

src/Drupal/Driver/DrupalDriver.php

@@ -2,14 +2,15 @@
 
 namespace Drupal\Driver;
 
+use Drupal\Driver\Cores\CoreAuthenticationInterface;
 use Drupal\Driver\Exception\BootstrapException;
 
 use Behat\Behat\Tester\Exception\PendingException;
 
 /**
  * Fully bootstraps Drupal and uses native API calls.
  */
-class DrupalDriver implements DriverInterface, SubDriverFinderInterface {
+class DrupalDriver implements DriverInterface, SubDriverFinderInterface, AuthenticationDriverInterface {
 
   /**
    * Track whether Drupal has been bootstrapped.
@@ -368,4 +369,22 @@ public function sendMail($body, $subject, $to, $langcode) {
     return $this->getCore()->sendMail($body, $subject, $to, $langcode);
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function login(\stdClass $user) {
+    if ($this->getCore() instanceof CoreAuthenticationInterface) {
+      $this->getCore()->login($user);
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function logout() {
+    if ($this->getCore() instanceof CoreAuthenticationInterface) {
+      $this->getCore()->logout();
+    }
+  }
+
 }