If you are in the US you can get full details of how to watch the movie here. At the moment you need a US credit card and IP address to be able to access the movie, but Sony should be making it available in other territories at some point. (Though I suspect that copies of the film will be available via alternative methods pretty quickly!)
When the studio stated a few days ago that they would not release the film online movie site IMDB was inundated with reviews of the film with it getting a perfect 10/10 rating even though nobody had actually seen it. It looks like the site has cleaned up a lot of the reviews in the interim..
Interestingly the online payments are handled by Stripe ..