Apple - How to install composer via homebrew

It's now possible to install composer running

brew install composer

Previous answer (for older versions):

It seems the solution was running:

brew tap homebrew/homebrew-php

and then

brew install composer

After that composer seems to be installed:

composer --version
Composer version 1.5.5 2017-12-01 14:42:57

Now as time passed, this works for me:

$ brew install composer