support private repos by adding auth_token key to yaml

[MennaEssa]

in order to support building applications with private dependencies , we've added support for github private repos by adding an extra auth_token key in the yaml file and sending it the in the authorization headers.

[micahsnyder]

Hi @MennaEssa I'm so sorry I didn't see your PR until now. Wow it's been a long time. You're welcome to ping on PR's if needed!

I'll check this out now.

[micahsnyder]

I imagine this works. But storing credentials in a file that goes in version control may get you in a lot of trouble, and it's not something you could use at all for recipes stored in a public repo, like https://github.com/Cisco-Talos/clamav-mussels-cookbook

It would be far safer to store the credential in an environment variable, and have the yaml provide Mussels at the environment variable name so Mussels could read the token from the environment variable.