For auth I forked my own build of the Passport hex. For uploads I used the Arc hex, and for SSL I used Letsencrypt though I eventually realized that Heroku charges $20/mo for SSL and I'm not accepting anything like credit cards yet so it hasn't warranted the expense. Awesome-elixir is a great source for libraries, and it's had everything I needed so far:

https://github.com/h4cc/awesome-elixir