I need to configure an "Accton MR3201A" access point running OpenWrt.
I want it to provide an open WiFi with an HTTP authentication webpage on which users must provide a username & password before being able to access the internet.
Is there an existing package (http://downloads.openwrt.org/snapshots/trunk/ar71xx/packages/) that allows this ?
There are a few captive portal solutions out there and the best solution depends on your flexibility, customization, and technology requirements.
Captive Portal Solutions:
I personally use a highly customized wifidog package and authserver which has been revamped from the ground up for our company. We were able to add per user and pooling bandwidth controls, custom user accounting data, WISPr support (patch from guys over at Coova, they do not host this patch anymore). And we're currently working on hooking squid support. We went with Wifidog as it was much easier to customize and ran at layer3 using iptables as opposed to chillispots layer2 solutions. But the best solution depends on the amount of time, effort and flexibility you would like.
References:
http://wiki.openwrt.org/doc/howto/wireless.hotspot
There is CoovaAP which is available for OpenWRT/ar71xx at http://downloads.openwrt.org/snapshots/trunk/ar71xx/packages/coova-chilli_1.2.9-1_ar71xx.ipk
It works, but the documentation on how to set it up is sparse at times. The documentation at www.coova.org is for somewhat older versions, so prepare for some experimentation in setting that up.
There are also other alternatives, but I do not have experience with them.