This seems to be the backing store:
https://www.jsonstore.io/9cfa993cd55704f2254949dc21a5f3a7a63...
With the ability to get a specific key from this style of URL:
And post to it to set a value.
There's no security though - anyone can overwrite any URL - e.g. in the console on that page:
pushJSON(endpoint + '/AAAAaaAaAaaAAaaAAAAAaAAAAaAAaAAaaaAAAAaA', 'http://www.example.com/');
AAaAAaAAaaaaaaaaaaAaAAaaAAAaAAaAAAaa = 110110110000000000101100111011011100 = [Some ID in the database]