fix: Fix the configuration of the extension when DBAL is not configured

Currently if you happen to not configure DoctrineDBAL, the extension
will append the types to the DBAL configuration resulting in an invalid
config, which will crash the booting of the Symfony app.

A typical scenario where DBAL may not be configured is if you an an
environment with in-memory tests, where DBAL is not used at all.

src/DependencyInjection/LeagueOAuth2ServerExtension.php

@@ -88,6 +88,13 @@ public function getAlias(): string
      */
     public function prepend(ContainerBuilder $container)
     {
+        // If no doctrine connection is configured, the DBAL connection should
+        // be left alone as adding any configuration setting with no connection
+        // will result in an invalid configuration leading to a hard failure.
+        if (!self::hasDoctrineConnectionsConfigured($container->getExtensionConfig('doctrine'))) {
+            return;
+        }
+
         $container->prependExtensionConfig('doctrine', [
             'dbal' => [
                 'connections' => null,
@@ -110,6 +117,23 @@ public function process(ContainerBuilder $container)
         $this->assertRequiredBundlesAreEnabled($container);
     }
 
+    private static function hasDoctrineConnectionsConfigured(array $configs): bool
+    {
+        foreach ($configs as $config) {
+            if (!isset($config['dbal'])) {
+                continue;
+            }
+
+            if (isset($config['dbal']['connections'])
+                && \count($config['dbal']['connections']) > 0
+            ) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
     private function assertRequiredBundlesAreEnabled(ContainerBuilder $container): void
     {
         $requiredBundles = [
@@ -227,7 +251,7 @@ private function configurePersistence(LoaderInterface $loader, ContainerBuilder
         }
 
         $persistenceConfig = current($config['persistence']);
-        $persistenceMethod = key($config['persistence']);
+        $persistenceMethod = $this->getPersistenceMethod($config);
 
         switch ($persistenceMethod) {
             case 'in_memory':
@@ -241,6 +265,18 @@ private function configurePersistence(LoaderInterface $loader, ContainerBuilder
         }
     }
 
+    private function isDoctrinePersistenceEnabled(array $config): bool
+    {
+        return 'doctrine' === $this->getPersistenceMethod($config);
+    }
+
+    private function getPersistenceMethod(array $config): ?string
+    {
+        $persistenceMethod = key($config['persistence']);
+
+        return \is_string($persistenceMethod) ? $persistenceMethod : null;
+    }
+
     private function configureDoctrinePersistence(ContainerBuilder $container, array $config, array $persistenceConfig): void
     {
         $entityManagerName = $persistenceConfig['entity_manager'];