Added missing security.yaml config

I just copied this over from https://symfony.com/doc/3.4/security/guard_authentication.html - since it probably just got lost somehow. When following the instructions at https://symfony.com/doc/current/security.html , you would still have `property: email` in there.

Author: ThomasLandauer

security/guard_authentication.rst

@@ -49,6 +49,64 @@ Don't forget to generate and execute the migration:
     $ php bin/console make:migration
     $ php bin/console doctrine:migrations:migrate
 
+Next, configure your "user provider" to use this new `apiKey`property:
+
+.. configuration-block::
+
+    .. code-block:: yaml
+
+        # config/packages/security.yaml
+        security:
+            # ...
+
+            providers:
+                your_db_provider:
+                    entity:
+                        class: App\Entity\User
+                        property: apiKey
+
+            # ...
+
+    .. code-block:: xml
+
+        <!-- config/packages/security.xml -->
+        <?xml version="1.0" encoding="UTF-8"?>
+        <srv:container xmlns="http://symfony.com/schema/dic/security"
+            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+            xmlns:srv="http://symfony.com/schema/dic/services"
+            xsi:schemaLocation="http://symfony.com/schema/dic/services
+                https://symfony.com/schema/dic/services/services-1.0.xsd">
+
+            <config>
+                <!-- ... -->
+
+                <provider name="your_db_provider">
+                    <entity class="App\Entity\User" property="apiKey"/>
+                </provider>
+
+                <!-- ... -->
+            </config>
+        </srv:container>
+
+    .. code-block:: php
+
+        // config/packages/security.php
+        $container->loadFromExtension('security', [
+            // ...
+
+            'providers' => [
+                'your_db_provider' => [
+                    'entity' => [
+                        'class' => 'App\Entity\User',
+                        'property' => 'apiKey',
+                    ],
+                ],
+            ],
+
+            // ...
+        ]);
+
+
 Step 2) Create the Authenticator Class
 --------------------------------------