startLogin(request: FederationLoginRequest): Promise<string>
Starts a sign-in with an account on the instance request.instance names,
and returns its /authorize page with the request, for
POST /api/federation/logins. Unless that instance is trusted, or someone
here already comes from it, the request must carry a valid invite, which is
claimed only once the account is made; completeLogin makes no
account without one.
request: FederationLoginRequest