I work for a small school where they want to open up the wifi network to students. The wifi network itself is already there, it's just not open to students. However they want to limit the usage for students by having a daily password expiry. The password of the day will be put on the school website and is only visible to teachers and the teachers will decide when students get the daily password. At the same time the teachers should also still have unlimited access with a password that doesn't expire.
I don't have access to the source code of the school website. It's a sort of CMS web application that's used by multiple schools. However it does support automatically loading an external file and automatically making an article out of it. So the system that generates that daily password should be able to automatically create a document that contains that daily password that it generated.
How would you set this up? I have googled a bit and what I need is I think a "captive portal" but I have no experience with that. What type of captive portal would meet those requirements? Would there be any free ones suitable for that or are they not so reliable and would it be better to go for a paid portal?