So I basically have two applications running, one at login.host.com and the other at app1.host.com. Now when a user signs in at login.host.com I want that application to create the auth cookie and redirect the user to app1.host.com, which can simply open the auth cookie. Now I set the domain (e.g. “.host.com”), salt and encryption key in Plug.Session (endpoint.exs) to the same values for the login app and app1. In config.exs I set the secret_key_base to the same value for both and set the url to [host: “host.org”] and [host: “login.host.org”] respectively. In the nginx proxy, I set “proxy_cookie_domain my_appX host.org;” for both, where my_appX is just the local (“upstream”) application name for nginx, i.e. my_app1 and my_app2. If I check the response cookie in firefox after logging in, it shows a different value for both applications as well. Any help is greatly appreciated!