fix: prevent loss of information when returning errors

Linked to:
- https://sentry.in.nuonet.fr/share/issue/5fa72de1b01b46bc81601958a2ff5fd2/
- https://sentry.in.nuonet.fr/share/issue/5a225f6400a647c0bbf1f7ea01566e63/

internal/proxy/director/layer/authn/oidc/client.go

@@ -69,7 +69,7 @@ func (c *Client) login(w http.ResponseWriter, r *http.Request, sess *sessions.Se
 	sess.Values[sessionKeyPostLoginRedirectURL] = postLoginRedirectURL
 
 	if err := sess.Save(r, w); err != nil {
-		director.HandleError(ctx, w, r, http.StatusInternalServerError, errors.New("could not save session"))
+		director.HandleError(ctx, w, r, http.StatusInternalServerError, errors.Wrap(err, "could not save session"))
 
 		return
 	}