Unified accounts service #289
Description
It would be really good to split authentication into its own service, that grants access to various environments depending on permissions.
The front-end logins can be different (depending on which environment the user is logging into) but they should still all hit the same endpoint for auth.
Example: I could log into staging.greenearthx.com or I could log into beta.greenearthx.com, and both should use the same accounts service so I don't need a separate account on each. Whether or not I am able to log in depends on the permissions my account has.