Make Cloudfront auth more configurable

[Vad1mo]

For continuous delivery reasons and improved security it would be better the secrets and other variables could be externalized.

The variables could be passed in as environment variables for example.

[payton]

This is an important point to bring up. Externalizing would be a good addition to the project.

Unfortunately, Lambda@Edge has some limitations in that it does not support environment variables. With that said, the next best thing may be to support AWS Parameter Store. This will require a bit more conversation on how to best implement it into the build process. Always open to suggestions on implementation and externalization methods.

[pldimitrov]

#38