We™re getting a lot of inquiries to have a ˜Billing Portal™ run out of Salesforce Communities. There are a number of approaches to achieving this. Many can be done with our app, Blackthorn Payments, out of the box. Here™s a doc on how to set it up.
If you want to kick off a subscription from a Closed Won Opportunity or CPQ Quote, you can use our Stripe Billing feature set, coming in February 2019. You can expose these Subscriptions & Invoices within a Community.
You can also use our Apex or REST APIs to make your own UI.
Contact firstname.lastname@example.org to learn more. If you need assistance in setting this up, Blackthorn can assist Salesforce Partners (SIs) or companies directly on a per-engagement basis.