External authentication

[termermc]

It should be possible to register an HTTP endpoint (or maybe script, depending on security implications) for a FriendNet room that handles authentication for a room instead of manual accounts and passwords. If configured, when a client attempts to connect to a room, the server will send the username, password and IP to the authentication endpoint, and it would return success or an error. This would make it possible to use external authentication, like a website or IRC account system, and not have to manually create or manage accounts. Since FriendNet accounts don't store any data other than credentials, it would be easy to implement this and basically have dynamic users based on external auth.

It might also be possible to configure external auth as a middleware to block certain IPs, but still use the native account system.

[termermc]

We could potentially implement an OAuth system enforced by the server later, but I'm personally not interested in doing that right now

[termermc]

For HTTP, it should allow configuring extra headers to send along with the request

[termermc]

Some other notes:

• It should be possible to have a "continue" or "passthrough" response that tells the server to use its own auth. This could be used to implement IP blocking middleware while still using the server's native accounts, or to only override auth on some rooms dynamically.
• You should be able to specify a global external authentication endpoint, but also be able to set it per-room in the config as well. On the config, you could set whether it should take precedence or if the global config should take precedence. That would be useful if the global config is a middleware and should run first.