Add Joomla Single-Sign-On (SSO) into InvoicePlane

We want to use Joomla logins for InvoicePlane. The unrelated people here do as well: [login to view URL] You need to: 1. build, test, and debug a production-ready solution that works for this. 2. provide me with the updated file(s) that I can use to make this work now 3. submit patches to the InvoicePlane open-source project that make this feature generally available for all InvoicePlane users (so, your patch needs to automatically NOT break installations that do not use Joomla)