For completely private services, the obvious answer is a VPN. But what about the ones that need to be “partially” public? Whether just read only, or with restrictions to publicly registered accounts.
For example, If I wanted to open up a git host where I allow public registrations so they can send issues/patches but can’t create repos (kinda impossible with pull requests but you get my point)
Is there any specific thing you can do, or do you just disable registrations completely except for something “out-of-band” (ask me on XYZ to create an account for you, git send-email, mirrors to public services, etc…)
Of course, individual software may have access control features built in, but as a whole, is there anything reasonably generic?
Imo a relatively sure way for “global” control would be setting up an SSO provider and managing access through that. Though that’s additional work and you’d still have to set the right settings in the application itself to how you want it.