Sorry for the late reply. My solution is based on wifidog installed on trunk OpenWRT with a custom written web portal and Splash screen management running in the cloud. The question about the CNA . . . IOS looks to see if it can connect to a number of different web pages to determine internet connectivity. If it cannot CNA opens and shows the Splash page. I am doing nothing clever, its all part of wifidog. The Splash page is responsive.
For fb or google+ authentication you will need to use the respective API and calls and ensure that the necessary URLs are open. Ipset is your friend here. All available for free.
You cannot force users to give a like or post comment, but you can prompt and have a skip button. This is the solution we have made. We can also host an advert and direct users here or custom URL. We log users MAC and logon details to ensure compliance with the law. User data can be exported and mailed as CSV file. This where fb and google+ logons are good as we get the users primary email address.
We now support public and private SSID's and the AR150 based Hotspot is perfect for small venues. We are now running on Linksys 1200AC and this router is a beast . . . its fast.
Its been a lot of effort and fun while working full time but I have a number of units running around Europe now and cheap at £99 per year unlike other vendors such as purple or wiman. I see one company asking for £99 per month to download all user records in CSV. Crazy!
I am looking for partners to sell my solution so get in touch if you are interested. You can source your own hardware and set your own prices. Set up takes around 15 mins if you know OpenWRT and vi and I email the web dashboard credentials. We have string support currently for English, Portuguese, Spanish and Vietnamese.
@leoh . . . its a lot of effort and hard work.