I haven’t had a chance to read all the posts yet, but currently this is our main thread on authentication in Phoenix:
It’s quite possible that different packages will be favoured by different people (for different reasons or apps).
We also have a list of starter templates and example apps here 
Phoenix_Guardian - An example implementation of authentication in Phoenix using Überauth and Guardian by Daniel Neighman.
Openmaize-Phoenix - Examples of using Openmaize authentication / authorization library in a Phoenix web application by David Whitlock.
Hope these threads are of some use to you
