enable account creation through mastodon OAuth

[hartsick]

part of my desire to create a simple forum was to allow for slower, longer lasting conversations for online communities centered around feed-based media (particularly Mastodon/Hometown, though could also work for Slack or Discord).

the forum is intended to supplement existing spaces or communities—for example, could sit at forum.logic.camp, if the main Mastodon instance is logic.camp. if this were the use case, having accounts be linked to (and probably only open to) members of that instance would be useful.

enter Mastodon OAuth and the Omniauth Mastodon strategy! using this, I could more firmly link account creation to the fediverse.

some questions I'm thinking about for this:

• given this use case, it makes sense to limit account access to certain Mastodon instances (likely singular, but could imagine multiple to form a sort of neighborhood. this idea and the core of this issue thanks to Darius Kazemi's run your own social)
• how do Mastodon and non-Mastodon authentication interact? should the forum be all or nothing? (eg a switch a moderator can flip to turn Oauth fully off or on?) this is a question of community and intended use more than technical