Wanted: Pre-Authorized Payment Solution

We're building a service for Decentraland users that requires a base payment + buffer amount. The base is predictable, and the buffer amount can vary and is only known when the service expires.

Where would I find a payment solution for a website (or have someone build one for us) that we can pre-authorize a total amount of ETH/ERC-20 tokens, and when the service expires (in x amount of time) the actual amount is debited, and any remaining from the pre-authorized amount is not?