Sorry to bump this topic! But I thought this was a good idea for a simple iot beginners project. I took the tips in this thread and soldered some AliExpress parts together.
The guest wifi password changes every night with a random generated 12 character string. A QR-code is generated on the Luci login page and also a simple text file in the www folder with the QR-code payload. The ESP8266 (nodemcu) together with a ST7789 LCD-screen refreshes the payload over the main wifi and the display generates a QR-code which a phone can scan.
I'll update this post later with a link to a github repo.
