I have two php applications: one hosted on example.com and one on example.org. Both applications are indispensable, means when a user uses application of example.com, it will use example.org too because a part of application is at example.com and another part is at example.org. But there is a problem. When user is using example.com and need a function of example.org, he goes to example.org, by clicking a button from example.com (and vice-versa) but he needs to login again (that's the problem).
How to auto-login user on example.org, when he is sent to example.org from example.com (usernames&passwords are the same for a user on both domain).
I want to be very secure.
Thank you so much!