Etherpad crash if HTTP header already sent

ep_laclasse/authenticate.js

@@ -140,7 +140,9 @@ exports.authFailure = function(hook_name, context, cb) {
   const url = `${baseUrl.toString()}?${urlParams.toString()}`;
 
   // redirect to the auth url
-  context.res.redirect(url);
+  try {
+    context.res.redirect(url);
+  } catch(e) {}
 
   laclasseLogger.warn('authFailure: Redirect to SSO: ',url);
   // signal that we have handled it