pert:
I think this is the library of choice for configuring the WiFi SSID and password:
GitHub - tzapu/WiFiManager: ESP8266 WiFi Connection manager with web captive portal
but it doesn't support additional configurations. You should be able to modify it as you like fairly easily.
According to a quick glance of the doco, it definitely can:
"You can use WiFiManager to collect more parameters than just SSID and password. This could be helpful for configuring stuff like MQTT host and port, blynk or emoncms tokens, just to name a few. You are responsible for saving and loading these custom values. The library just collects and displays the data for you as a convenience."
A gold star for you, thanks so much!