Adopted example to be multi-node ready by using Redis for tokens instead of plain Map

I like you sample implementation for its simplicity, but it would lack the ability to scale horizontally when used like this is a real REST application with multiple running nodes. You'd have to sync the token maps somehow as you'd never know to which node your next request might go.

This is why I exchanged your map repository store with one that is using a Redis key-value store which would in a REST-friendly way allow for syncing the tokens among nodes (via file system essentially).

Feel free to merge it into your own repo or just pick what you like best. Cheers, Björn