feature #189 Add response message when not authenticated (VincentLanglet)

This PR was squashed before being merged into the 0.4-dev branch.

Discussion
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Add response message when not authenticated

Hi `@chalasr`

This give something more friendly message in case of errors.

From
<img width="475" alt="image" src="https://github.com/thephpleague/oauth2-server-bundle/assets/9052536/a699fcf7-7345-49a1-8c05-0fc9281d82a5">
To
![image](https://github.com/thephpleague/oauth2-server-bundle/assets/9052536/937bddc1-140a-41d2-a4ec-0c8495aa8c3b)

Can consider it
Closes #188

Commits
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d554d8d Add response message when not authenticated

Author: chalasr

src/Security/Authenticator/OAuth2Authenticator.php

@@ -60,7 +60,7 @@ public function supports(Request $request): ?bool
 
     public function start(Request $request, ?AuthenticationException $authException = null): Response
     {
-        return new Response('', 401, ['WWW-Authenticate' => 'Bearer']);
+        return new Response($authException?->getMessage() ?? 'Authentication required', 401, ['WWW-Authenticate' => 'Bearer']);
     }
 
     /**