Seems like a standard email-username-password ought to be an option
Topic on Project:Support desk
@Riventree: What is a "dev forum"? Neither Github nor Phabricator are "dev forums". See Phabricator what Phab is [not].
I reckon you're referring to https://discourse-mediawiki.wmflabs.org/ and yeah, they are at the moment the only options. Actually, in practice this means that you must have a Wikimedia account (which you do, Riventree), because you can log into Phabricator as that. Which means it's a two-step process, but does work.
When Discourse makes it into production (i.e. off wmflabs.org) it'll be a one-step thing and you'll still only need your main Wikimedia username.
The reason for not supporting Wikimedia login directly from Discourse is phab:T124691.