Topic: Uplink access vouchers and (optional) captive portal?

Guys, I am slowly chewing through OpenWRT learning process, as I happened to become a neighbourhood-wide network admin. Solely due to the lack of any other fool around.

We have a network of several APs implemented on small linux boxes (GL.iNet 150/300 Mbps routers) and one master router (TP-LINK WDR4310), doing uplink load balance and such. Now, I am looking for a hint, how to achieve the uplink (internet) access control through vouchers or similar stuff.
Ideally, the network inside would be all open, without passwords, full roaming and access to internally hosted services (we have fast ethernet or wifi everywhere), while the access to external services would be limited to those who pay their cost share (this is non-profit community initiative).

So my idea is that people would be assigned 30-day valid vouchers, allowing them to access the gateway, optionally  through a captive portal, as it is often done in public premises. Is there any such module available for OpenWRT, or should I look for something else?

Other than that, I will go for unique logins/passwords, but then it gets complex, as we want to keep some free access for guests etc.

Anyway, all suggestions welcome.

Re: Uplink access vouchers and (optional) captive portal?

This question is not specific to OpenWrt, you will probably find more information in specific forums about captive portals.