Dynamically Assigning Adafruit IO credentials to Adafruit MQTT object

[Pius171]

• Arduino board: ESP8266

• Arduino IDE version (found in Arduino -> About Arduino menu): 1.8.16

• List the steps to reproduce the problem below (if possible attach a sketch or
  copy the sketch code in too): LIST REPRO STEPS BELOW
  I want to be able to dynamically assign my MQTT credentials. I want to store them in a file then read them in the setup function and assign them to my Adafruit MQTT object. I have looked through the library files but I can't find a way to do it.

In short, I want to be able to change my Adafruit io credentials without having to change them manually from the code.

Thank you.