(Source)
You can create a QR code that allows someone to join a wifi network of your choosing.
The format of the QR code is:
WIFI:S:<SSID>;T:<WEP|WPA|blank>;P:<PASSWORD>;H:<true|false|blank>;;
H is a setting that indicates if the network is hidden or not.
Can always use a tool like https://www.qr-code-generator.com/, if the programmatic generation is not needed.