Environment variables can now be used to configure any
config property including the feeds list.
This makes it easier to use in environments without access
to config files like GCR. Some may prefer not to have a separate
config file as well.
Also added build metadata to the docker image and binaries.
Often you want to expose your library publicly, which requires
authentication to prevent unknown users from seeing your
content.
In my case, I also expose the library on a local domain using a local DNS server which doesn't have these security issues.
This change adds a `local_only` option to the feed auth
config which will only supply the provided username/password
when the request comes from a private IP address.
Omitting `local_only` or setting to false will keep the current
logic of sending the credentials no matter the origin of the
request.
