OpenWRT/LEDE Captive Portal with Usage Vouchers

I need a OpenWRT or LEDE-based captive portal configuration that allows anonymous user logins using pre-established voucher codes with data and time limits for Internet access. For example, a user should be able to connect with a multiple-use voucher code for 1GB of data transfer valid for up to 12 months from first use. By 'anonymous,' I mean that I only want to require the voucher code to begin a session -- I do not need users to create individual accounts to redeem them. It is possible that a single code may be simultaneously shared with multiple devices. Of course, all data should be subtracted from the bucket. The firewall rules should allow access to the local IP range (i.e. which don't require external routing) without requiring a login or using any data. The router should also serve the captive portal page and the authentication duties. The captive portal screen should be modifiable by the sysadmin, and the sysadmin will be able to load a list of voucher codes with data limits into any reasonable SQL table or CSV file on the router. If possible, I would like to use as much existing open-source software as possible: OpenWRT or LEDE, Open/FreeRADIUS, Wifidog or Coovachili, etc. I am open to other solutions. The deliverable will be a functioning set of packages and configuration files to be installed in an OpenWRT or LEDE environment.