Well, it's entirely up to you what login mechanism you want to use, so if Github isn't what you want, then by all means don't use it. You can be completely self-reliant using email login, or eventually PGP login. But some people find Google and Github login convenient.
FWIW we're currently working on a change that will allow you to attach multiple such "identities" to a single account, after which we plan to open up the door to a lot more authentication providers, including other "open" federated options like OpenID or Shibboleth (as well as popular proprietary services like Twitter, Facebook, etc. -- again, it's up to each user to decide what's most convenient for them).
Probably at some point you'll be able to host your own IDP as a Sandstorm app, if that's what you want. Other Sandstorm servers would be able to rely on that IDP as well, so it meets the federated requirement.
FWIW we're currently working on a change that will allow you to attach multiple such "identities" to a single account, after which we plan to open up the door to a lot more authentication providers, including other "open" federated options like OpenID or Shibboleth (as well as popular proprietary services like Twitter, Facebook, etc. -- again, it's up to each user to decide what's most convenient for them).
Probably at some point you'll be able to host your own IDP as a Sandstorm app, if that's what you want. Other Sandstorm servers would be able to rely on that IDP as well, so it meets the federated requirement.