Hi,
I'll be pleased to complete this project for you. Let me introduce myself: I'm a CCIE (R&S) certified network and systems specialist with 7+ years of experience in developing, configuring, and maintaining complex networks for large enterprises.
I'm passionate about WiFi Captive Portals and have extensive hands-on experience in their design and setup. Although I haven't done an OpenWRT based captive portal yet, I have setup many Linux based captive portals written in PHP for Mikrotik, Ubiquiti and OpenMesh devices and also have done RADIUS integration for AAA services. Also, I have created captive portals that support social media logins. I can share with you my experiences of working with these devices. If you still want to proceed with OpenWRT I'm sure I'll be able to setup that for you as well. I already have test gear available with me.
As proof of similar Freelancer projects that I have completed or are under progress please check out the following links:
https://www.freelancer.com/projects/php/Unifi-Custom-Portal-with-Email/
https://www.freelancer.com/projects/graphic-design/social-media-integration-wifi-captive/
https://www.freelancer.com/projects/graphic-design/create-customizable-Wifi-landing-page/
https://www.freelancer.com/projects/php/internet-hotspot-unifi-router/
Do send me a message and we can discuss this further.