Dynamic SSID + Password from ESP8266WiFi
The const keyword there does not force the data you call it to be constant, it only forbids certain assignments with the parameters inside that function but it's just superfluous in most cases. Meaning you can call it with input you got from serial or some other source (for ex. setup page accessible from hotspot->Store in EEPROM->Next boot connect to set WiFi AP). There's also a nice StackOverflow thread about this here and why it's not actually a good idea in many cases.