diff --git a/src/Api/Field/AclConfiguration.php b/src/Api/Field/AclConfiguration.php
index 42b743e..3f5e462 100644
--- a/src/Api/Field/AclConfiguration.php
+++ b/src/Api/Field/AclConfiguration.php
@@ -10,24 +10,31 @@
 use GraphQL\Type\Definition\EnumType;
 use GraphQL\Type\Definition\Type;
 
+/**
+ * @phpstan-import-type PermissiveFieldsConfig from FieldInterface
+ */
 abstract class AclConfiguration
 {
-    public static function build(Acl $acl, EnumType $roleType): array
+    /**
+     * Return the single field configuration, including its name.
+     *
+     * @return PermissiveFieldsConfig
+     */
+    public static function build(Acl $acl, EnumType $roleType): iterable
     {
-        return
-            [
-                'name' => 'aclConfiguration',
-                'type' => Type::nonNull(Type::listOf(Type::nonNull(_types()->get(AclResourceConfigurationType::class)))),
-                'description' => 'User friendly configuration of the ACL',
-                'args' => [
-                    'roles' => Type::nonNull(Type::listOf(Type::nonNull($roleType))),
-                ],
-                'resolve' => function ($root, array $args) use ($acl): array {
-                    $roles = $args['roles'];
-                    $result = $acl->show(new MultipleRoles($roles));
+        yield 'aclConfiguration' => fn () => [
+            'name' => 'aclConfiguration',
+            'type' => Type::nonNull(Type::listOf(Type::nonNull(_types()->get(AclResourceConfigurationType::class)))),
+            'description' => 'User friendly configuration of the ACL',
+            'args' => [
+                'roles' => Type::nonNull(Type::listOf(Type::nonNull($roleType))),
+            ],
+            'resolve' => function ($root, array $args) use ($acl): array {
+                $roles = $args['roles'];
+                $result = $acl->show(new MultipleRoles($roles));
 
-                    return $result;
-                },
-            ];
+                return $result;
+            },
+        ];
     }
 }
diff --git a/src/Api/Field/FieldInterface.php b/src/Api/Field/FieldInterface.php
index fabdb28..25c4adf 100644
--- a/src/Api/Field/FieldInterface.php
+++ b/src/Api/Field/FieldInterface.php
@@ -4,13 +4,43 @@
 
 namespace Ecodev\Felix\Api\Field;
 
+use GraphQL\Language\AST\FieldDefinitionNode;
+use GraphQL\Type\Definition\FieldDefinition;
+use GraphQL\Type\Definition\ResolveInfo;
+use Mezzio\Session\SessionInterface;
+
 /**
  * Represent a single field configuration.
+ *
+ * Below, we re-define some type coming from webonyx/graphql, because our `\GraphQL\Doctrine\Types::get()`
+ * is too poorly typed to match the correctness of webonyx/graphql. If we are able to fix our typing one day,
+ * then we should remove those overrides below.
+ *
+ * @phpstan-import-type FieldType from FieldDefinition
+ * @phpstan-import-type ComplexityFn from FieldDefinition
+ * @phpstan-import-type VisibilityFn from FieldDefinition
+ *
+ * @phpstan-type PermissiveArgumentListConfig iterable<mixed>
+ * @phpstan-type FieldResolverWithSessionInterface callable(mixed, array<string, mixed>, SessionInterface, ResolveInfo): mixed
+ * @phpstan-type PermissiveUnnamedFieldDefinitionConfig array{
+ *      type: FieldType,
+ *      resolve?: FieldResolverWithSessionInterface|null,
+ *      args?: PermissiveArgumentListConfig|null,
+ *      description?: string|null,
+ *      visible?: VisibilityFn|bool,
+ *      deprecationReason?: string|null,
+ *      astNode?: FieldDefinitionNode|null,
+ *      complexity?: ComplexityFn|null
+ *  }
+ * @phpstan-type PermissiveDefinitionResolver callable(): PermissiveUnnamedFieldDefinitionConfig
+ * @phpstan-type PermissiveFieldsConfig iterable<string, PermissiveDefinitionResolver>
  */
 interface FieldInterface
 {
     /**
      * Return the single field configuration, including its name.
+     *
+     * @return PermissiveFieldsConfig
      */
-    public static function build(): array;
+    public static function build(): iterable;
 }
diff --git a/src/Utility.php b/src/Utility.php
index d003129..00485cd 100644
--- a/src/Utility.php
+++ b/src/Utility.php
@@ -8,7 +8,7 @@
 use GraphQL\Doctrine\Definition\EntityID;
 use ReflectionClass;
 
-abstract class Utility
+final class Utility
 {
     /**
      * Returns the short class name of any object, eg: Application\Model\Calendar => Calendar.
@@ -124,4 +124,28 @@ public static function getCookieDomain(string $input): ?string
 
         return $cookieDomain;
     }
+
+    /**
+     * Concatenate all given iterables into a new iterator that yields key/value pairs exactly as if we iterated through each iterable sequentially.
+     */
+    public static function concat(iterable ...$iterables): iterable
+    {
+        foreach ($iterables as $iterable) {
+            foreach ($iterable as $k => $v) {
+                yield $k => $v;
+            }
+        }
+    }
+
+    /**
+     * Return a new iterable with only key/value pairs that match the given keys.
+     */
+    public static function filterByKeys(iterable $things, string ...$keyToKeep): iterable
+    {
+        foreach ($things as $k => $v) {
+            if (in_array($k, $keyToKeep, true)) {
+                yield $k => $v;
+            }
+        }
+    }
 }
diff --git a/tests/UtilityTest.php b/tests/UtilityTest.php
index 1fe9f11..e6fbfa3 100644
--- a/tests/UtilityTest.php
+++ b/tests/UtilityTest.php
@@ -4,6 +4,7 @@
 
 namespace EcodevTests\Felix;
 
+use ArrayIterator;
 use Ecodev\Felix\Model\Model;
 use Ecodev\Felix\Utility;
 use EcodevTests\Felix\Blog\Model\User;
@@ -178,4 +179,27 @@ public function testGetCookieDomain(string $input, ?string $expected): void
         $actual = Utility::getCookieDomain($input);
         self::assertSame($expected, $actual);
     }
+
+    public function testConcat(): void
+    {
+        $iterable = new ArrayIterator([1 => 'one', 'a' => 'overridden', 'c' => 'c']);
+        $actual = Utility::concat(['a' => 'a', 2 => 'two'], $iterable);
+
+        self::assertSame([
+            'a' => 'overridden',
+            2 => 'two',
+            1 => 'one',
+            'c' => 'c',
+        ], iterator_to_array($actual));
+    }
+
+    public function testFilterByKeys(): void
+    {
+        $things = new ArrayIterator(['a' => 'a', 'b' => 'b', 'c' => 'c']);
+
+        self::assertSame(['a' => 'a'], iterator_to_array(Utility::filterByKeys($things, 'a')));
+        self::assertSame(['a' => 'a', 'c' => 'c'], iterator_to_array(Utility::filterByKeys($things, 'c', 'a')));
+        self::assertSame([], iterator_to_array(Utility::filterByKeys($things, 'unknown-key')));
+        self::assertSame([], iterator_to_array(Utility::filterByKeys($things)));
+    }
 }