Set & load environment variables in a phoenix app

I have found another example

1.- Create a file .env in you main folder

2.- Add the env variables in the .env file

# Example:
# MyApp/.env file
export GITHUB_CLIENT_ID="testID"
export GITHUB_SECRET_CLIENT_ID="testSecretID"

3.- Run source .env and every time it is modified, execute the command again, maybe in reboot too

4.- What is really important - don't forget to add your secret files to MyApp/.gitignore

# add this at the end
/.env

5.- Run phoenix server mix phx.server or mix phoenix.server

You can test it with

iex -S mix phoenix.server

iex> System.get_env("GITHUB_CLIENT_ID")
"testID"

Links of help:

Environment variable error
Documentation of config

There are two main glitches with what you are trying to do:

First of all, you are trying to instruct mix to configure oauth OTP application, while what you need is to configure your own one:

config :my_app, :oauth,
  github_client_id: "(CLIENT ID)",
  github_client_secret: "(SECRET)"

Now in your main config you might do:

config :ueberauth, Ueberauth.Strategy.Github.OAuth,
   client_id: Application.get_env(:my_app, :oauth)[:github_client_id],
   client_secret: Application.get_env(:my_app, :oauth)[:github_client_secret]

The second glitch is that GITHUB_CLIENT_ID is an atom, and you are trying to access it lately as a string. In general, one should not use atom names starting with an uppercase since they kinda reserved for modules names.

On the other hand, you might still use System.get_env/2 (with your config.ex,) assuming the values were previously put there in environment:

prod.secret.exs (as it is still plain Elixir)

System.put_env("GITHUB_CLIENT_ID", "(CLIENT ID)")
System.put_env("GITHUB_CLIENT_SECRET", "(CLIENT SECRET)")