bundle install --verbose on Bundler versions 1.12+, you might see errors of the form
HTTP 403 Forbidden https://username:email@example.com/versions
These errors are not fatal, Rails LTS should still be installed correctly. This has been tested with all Bundler versions 1.12.x and 1.13.x.
Since version 1.12, Bundler includes a performance optimization called "compact gem index". Our gem server does not support this.
When trying to access this new index our web server will return a 403. Bundler will log this to its output, but then fall back to using the old style index and proceed as usual.