I've been working some Mage2 builds locally and I can't fathom the correct way to handle auth.json and Composer access details.
I run all of my projects from ~/webdev/vhosts/ with each project having it's own virtualhost and folder.
As everything is run under the same user (it's my local machine) they all look to ~/.composer/auth.json for access details and this breaks as each project has it's own access keys for different repositories.
Magento comes with an auth.json in the root and also uses var/composer_home/auth.json but it seems that neither of these are loaded when using the composer command.
I've been unable to find an option for Composer to use a specific auth.json file.
How does everyone else deal with Composer access details?