provision new user with ssh key

[zoezhangmattr]

i am new to this functionality, i was wondering what is the good way to provision another user, for example macadmin , (i know the existent default user is ec2-user), and let it have the ability to consume ssh key like ec2-user as well. is it using the module or user-data. and what is the lifecycle of it. does it provision the user before instance is ready. so that i can use this user to ssh to the mac instance.

any guidance is appreciated. thanks a lot.