This is a general question seeking guidance for the best practice(s) on implementing a Single Sign On (SSO) across many various installations of the same application.
The hypothetical example I would like to pose - imagine you have 200 Wordpress installations / websites that you manage. In order to log into each environment, there's a unique username/password entry for each environment's database. When signing in, the authentication is against an environment-specific database where the query runs against your users table. What would be the appropriate technology(ies) to allow:
Me, as an administrator, the ability to log in one time, and hop from environment to environment. Let's assume each environment runs on different domains, such as client1.com/admin and client2.com/admin
My client, client #1, should be able to sign into their environment, but not automatically gain access to environments 2 and 3...
More context: I am building an application for an agency of several hundred employees. Each installment of the application will be a single-tenant database. I need a solution to allow for each employee to log in once, and jump from environment to environment, while still allowing the application to maintain it's own "local" user database for the specific clients (non-employees of the agency) who will use the application. I am also trying to wrap my head around how an ACL works in such an implementation.
Any leads, suggestions, or feedback are greatly appreciated!