add authentication to api

https://github.com/riverrun/comeonin
https://github.com/ueberauth/ueberauth

- https://github.com/ueberauth/ueberauth_example
- https://ueberauth-example.herokuapp.com/

GuardianDB is useful for storing token/info in the DB, mentioned in API tutorial below
- https://github.com/ueberauth/guardian_db

Install Guardian Steps:
- https://medium.com/@zacharykuhn/setting-up-a-phoenix-app-with-guardian-1-0-411ff3195adb

Auth Tutorial
- https://blog.codeship.com/ridiculously-fast-api-authentication-with-phoenix/
- https://medium.com/@zacharykuhn/setting-up-a-phoenix-app-with-guardian-1-0-411ff3195adb

https://github.com/ueberauth/guardian
Blog tutorials from the creators of Guardian:
- http://blog.overstuffedgorilla.com/simple-guardian/
- http://blog.overstuffedgorilla.com/simple-guardian-api-authentication/
- http://blog.overstuffedgorilla.com/simple-guardian-permissions/
- http://blog.overstuffedgorilla.com/simple-guardian-multiple-sessions/
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UeberAuth & Guardian Example App
- https://github.com/hassox/phoenix_guardian
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https://elixirschool.com/en/lessons/libraries/guardian/
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https://medium.freecodecamp.org/authentication-using-elixir-phoenix-f9c162b2c398
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https://medium.com/brightergy-engineering/jwt-authentication-based-api-in-phoenix-6c4b51909b19
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4 Step Process to add ComeOnIn and Guardian to a ToDo app
1. https://medium.com/@Stephanbv/elixir-phoenix-lets-code-authentication-todo-application-part-1-599ee94cd04d#.5ws457x2y
2. https://medium.com/@Stephanbv/elixir-phoenix-lets-code-authentication-todo-application-part-2-f52348c2b32f
3. https://medium.com/@Stephanbv/elixir-phoenix-lets-code-authentication-todo-application-part-3-acb879d8816
4. https://medium.com/@Stephanbv/elixir-phoenix-a-todo-and-user-relationship-todo-application-part-4-7c2d80d22dea #