Let's Control It

Use of an ibutton reader in place of rfid reader

I expect you would have to figure that one out yourself. I do not think they are used as much as Rfid.
First thing to check would be the connection, I have not looked at them for a long time, but all they had then was Serial interface which could be adapted to USB. Look for an arduino compatible reader and plugin.
You might be able to adapt the arduino plugin to ESPEasy.

iButtons are usually 1-wire interface, the same as the 1-wire thermometers (DS18b20).

I do wish ESPEasy had better generic 1-wire support, including support for the 1-wire GPIO chip.