It seems that I can configure a RADIUS accounting server in OpenWrt, however, I have not found any additional information how to use it ( URL: wiki.openwrt.org/doc/uci/wireless#wpaenterpriseaccesspoint ).

I want to use WPA2 EAP to authenticate users.

Is there a way to control the IP address which is provided to a user via RADIUS in OpenWrt. I would like to assign always the same IP address to a user and I would like to be able to log the session time and IP address for each user.

RADIUS supports the "Framed-IP-Address", but can I use it with OpenWrt?

Is there any other solution to log user sessions, including IP address and time of the session?

I have already contemplated to use a different VLAN for every user, however, my box only supports 15 VLANs; I need to handle around 40 users in a network with 8 APs.

Any proposal is very much appreciated.

Radius dos not provide an IP adrs. However, it can control the allowed quotas (traffic, connection time etc.) for a specific IP.
Your requirements might be best satisfied using a "Captive Portal". coova-chilli is best, but also the most complicated to set up.

Thanks a lot for you reply.

Well, actually you can use the "Framed-IP-Address" option either to inform RADIUS about the IP address used by a border device or to receive an IP address which you can assign to the client.

See e.g. dabbeljudabbeljudabbeljuDot     juniper.net/documentation/en_US/junos/topics/concept/subscriber-management-dual-stack-ipv4-address-negotiation-framed.html

This one is an example how a freeradius server can be configured with a  "Framed-IP-Address". Have a look at "Add Test User" in wiki.opnsense.org/manual/how-tos/accounting.html

Sorry, it seems I can not post complete links here, hope you can find it anyway.

I know the captive portal, however, it is an ongoing source for problems because it does not reliably open on all devices. That's why I am investigating EAP to move away from the captive portal. Actually, you have some more benefits from using WPA EAP.

As I did lot of customized solutions (i.g.hotspots) containing coova-chilli, I would be very interested in an example for ".... it does not reliably open on all devices".