diff --git a/backend/app/Controllers/AuthController.php b/backend/app/Controllers/AuthController.php
index 2ab46c8..0794f10 100644
--- a/backend/app/Controllers/AuthController.php
+++ b/backend/app/Controllers/AuthController.php
@@ -10,9 +10,11 @@ use App\Exceptions\BadRequestException;
 use App\Exceptions\UnauthorizedException;
 use App\Middleware\AuthMiddleware;
 use App\User\User;
+use DomainException;
 use Psr\Http\Message\ResponseInterface;
 use Psr\Http\Message\ServerRequestInterface;
 use Slim\Psr7\Response;
+use Throwable;
 
 class AuthController
 {
@@ -36,24 +38,13 @@ class AuthController
                     password: $body['password'] ?? null,
                 ),
             );
-        } catch (BadRequestException $exception) {
-            return $this->jsonResponse(
-                new Response(400),
-                ['error' => $exception->getMessage()],
-                400,
-            );
-        } catch (UnauthorizedException $exception) {
-            return $this->jsonResponse(
-                new Response(401),
-                ['error' => $exception->getMessage()],
-                401,
-            );
+        } catch (Throwable $exception) {
+            return $this->errorResponse($exception);
         }
 
         $session = $this->createSession->execute($user);
 
         $response = $this->jsonResponse(
-            new Response(200),
             ['user' => $this->buildUserPayload($user)],
             200,
         );
@@ -98,14 +89,12 @@ class AuthController
 
         if (! $user instanceof User) {
             return $this->jsonResponse(
-                new Response(401),
                 ['error' => 'unauthenticated'],
                 401,
             );
         }
 
         return $this->jsonResponse(
-            new Response(200),
             ['user' => $this->buildUserPayload($user)],
             200,
         );
@@ -120,16 +109,38 @@ class AuthController
     }
 
     private function jsonResponse(
-        ResponseInterface $response,
         array $data,
         int $status,
     ): ResponseInterface {
-        $response = $response->withStatus($status);
+        $response = new Response($status);
         $response->getBody()->write(json_encode($data));
 
         return $response->withHeader('Content-Type', 'application/json');
     }
 
+    private function errorResponse(Throwable $exception): ResponseInterface
+    {
+        if ($exception instanceof BadRequestException) {
+            return $this->jsonResponse(
+                ['error' => $exception->getMessage()],
+                400,
+            );
+        }
+        if ($exception instanceof UnauthorizedException) {
+            return $this->jsonResponse(
+                ['error' => $exception->getMessage()],
+                401,
+            );
+        }
+        if ($exception instanceof DomainException) {
+            return $this->jsonResponse(
+                ['error' => $exception->getMessage()],
+                409,
+            );
+        }
+        throw $exception;
+    }
+
     private function parseBody(ServerRequestInterface $request): array
     {
         $contentType = $request->getHeaderLine('Content-Type');