Support authenticated urls for http_archive (.netrc or other)

I'm was attempting to migrate mid-size a Bazel repo over, but immediately hit a key sticking point - I need to be able to fetch pre-built binaries from an authenticated artifactory instance. Bazel simply allows using .netrc (similar to `curl -c`), which works quite well and is standard. Having similar support would be ideal, but anything allowing access to authenticated remote urls is a requirement for us.