Both terminals of the KL International Airport (called KLIA and KLIA2) provides free wifi access to anyone
The network is simply called "Airport WiFi"
You can connect to it without needing to provide any information like email or passport #
Access is good for 24 hours
Some areas have stronger signals than others so you may need to walk around a bit to find the best spot
It's great for calling Grab. But the strength decreases fast outside the terminal building so do it while inside
In addition to the free wifi, there is also a premium version of it for 8RM for 24 hours. This is equal to around $2 US dollars. The premium version is faster but I've never had issues with the free one for even watching videos