I tried to register for an account on Open VSX. That took my to the Eclipse Foundation account flow, which I completed (this part of the flow was confusing since it told me my password was "invalid," but it seems like I really just needed to go to my email and click a validation link that wasn't hinted in the enrollment flow).
However, when I click the "Log in with Eclipse" button on my settings page on Open VSX, I get an HTTP 500:
This seems potentially related to #1335. Like that issue, I tried cycling my sessions/using an incognito browser session, but had no luck.