diff --git a/budget/tests.py b/budget/tests.py
index 9eea518..0f7c2a2 100644
--- a/budget/tests.py
+++ b/budget/tests.py
@@ -289,6 +289,11 @@ class BudgetTestCase(TestCase):
         self.assertTrue(models.Project.query.get("demo") is not None)
 
     def test_authentication(self):
+	# try to authenticate without credentials should redirect
+	# to the authentication page
+	resp = self.app.post("/authenticate")
+	self.assertIn("Authentication", resp.data)
+
         # raclette that the login / logout process works
         self.create_project("raclette")
 
diff --git a/budget/web.py b/budget/web.py
index 0b302cd..77de026 100644
--- a/budget/web.py
+++ b/budget/web.py
@@ -72,7 +72,14 @@ def authenticate(project_id=None):
     if not form.id.data and request.args.get('project_id'):
         form.id.data = request.args['project_id']
     project_id = form.id.data
-    project = Project.query.get(project_id)
+    if project_id is None:
+        #User doesn't provide project identifier, return to authenticate form
+        msg = _("You need to enter a project identifier")
+        form.errors["id"] = [msg]
+        return render_template("authenticate.html", form=form)
+    else:
+        project = Project.query.get(project_id)
+
     create_project = False  # We don't want to create the project by default
     if not project:
         # But if the user try to connect to an unexisting project, we will