Still no dice. I have the following options but none of them show subscriptions or upcoming invoices, only my most recently paid one. Nor does "update card" show any current form of payment that can be cancelled or removed.
I think the problem is the CRM was sending the payment to Authorize.net as a single payment each month. Authorize.net doesn't know it's a subscription. I'll have to figure out a way to enable users to cancel.