Read/Write Payment Secrets

[danirabbit]

The authenticator will need to be able to read and write payment method secrets so that users are presented with a list of their already saved payment methods and the ability to add or use a different one

There's a prototype for this here: https://github.com/elementary/appcenter/tree/save-payment-info

[danirabbit]

Since the authenticator needs to be cross platform, it can't rely on the existence of the wallet, which is specific to Pantheon.

It sounds like secrets are stored per-app in the container, so tokens generated by the authenticator won't be able to be fetched by the wallet.

So this means we need to have a non-charge interface for the authenticator which the wallet can call to create payment tokens.

We'll also need maybe a D-Bus interface for the wallet to get non-secret data about cards so that it can list them in its UI.

The authenticator will be the only UI on the system for generating and using payment tokens and storing payment secrets