set xsrf cookie on base url (#612)

avoids collisions across a given host

Author: minrk

jupyter_server/serverapp.py

@@ -356,6 +356,10 @@ def init_settings(
 
         # allow custom overrides for the tornado web app.
         settings.update(settings_overrides)
+
+        if base_url and "xsrf_cookie_kwargs" not in settings:
+            # default: set xsrf cookie on base_url
+            settings["xsrf_cookie_kwargs"] = {"path": base_url}
         return settings
 
     def init_handlers(self, default_services, settings):