Challonge has an API to allow integration into websites. Started messing around with it. Allows for signup and score reporting directly through your website. Unfortunately the API does not yet support the type of tournament that the Rocket League tournament is doing, so all I can do is display it. Anyway, check it out and let me know what you think.
There is a widget at the bottom of the page to sign up for open tournaments or it turns to a report button if ongoing.