This error is raised if HTTP authentication is required, but not provided.
# File bundler/fetcher.rb, line 46
def initialize(remote_uri)
remote_uri = filter_uri(remote_uri)
super "Authentication is required for #{remote_uri}.\n" \
"Please supply credentials for this source. You can do this by running:\n" \
"`bundle config set --global #{remote_uri} username:password`\n" \
"or by storing the credentials in the `#{Settings.key_for(remote_uri)}` environment variable"
end