The OAuth Server Application has to be activated in Phabricator. Once activated Phragile needs to be registered as an OAuth application. There are two fields to fill out when creating a new OAuth application. "Name" should be "Phragile" and "Redirect URL" should be "http://our-phragile-domain/login" (we don't know yet what the domain will be but it can be changed later on anyway). This will generate an OAuth Client ID and an OAuth Client Secret which Phragile needs in order for the OAuth login mechanism to work.
See discussion in T90489
(we need this solved before the hackathon in Lyon) - thanks.