I have been contacted several times in regards to my captive portal post. In India there seems to be a surge in popularity for restaurants to have an open WiFi that prompts a user to open up a menu/splash page. The caveat being the legal issues encountered when providing free, open wireless internet. In order to avoid legal issues, the device that broadcasts must be disconnected from the internet. Although I am curious if just blocking internet access for those connecting is enough.
It seems like an interesting issue to tackle, but I think creating something out of a WiFi captive portal would be like hammering a square peg through a round hole. It might work (if given enough time and effort), but in the end, it is probably not the right tool for the job.
While writing this post, I was reminded how Google appears to be tackling this problem. On my Android phone, I let the NSA spy on my whereabouts by enabling location services. It also lets my wife pinpoint where I am physically located. With it enabled, I can visit most shops in my area and get a Google maps prompt with the business information, reviews, and a few pictures. (Side note: if you appear in court over a childish/dumb action, you validate the judge’s decision when you post a negative review of the court house. Also please do not butcher the English language when trying to review places.)
Utilizing GPS location as well as having an app that provides the information seems like the best route to go in this circumstance. An alternative would be to have an app with WiFi credentials hardcoded in, listen for when a WiFi connection is made, check to see if it matches a predefined SSID, and attempt to communicate with a local app server to process data. Of course doing something like that is outside the scope of my tutorials.