Use Environment Variables and Avoid Config Step

[nelsonic]

At present the README.md recommends using Environment Variables but it requires you to add config settings to your config.exs:

We could avoid the step and just inform people they must have GITHUB_CLIENT_ID and GITHUB_CLIENT_SECRET defined in order for the package to work.

[nelsonic]

Thinking of raising an error if the environment variables are undefined:

iex> raise ArgumentError, message: "Environment variables GITHUB_CLIENT_ID and GITHUB_CLIENT_SECRET undefined"

see: https://hexdocs.pm/elixir/Exception.html and: https://elixir-lang.org/getting-started/try-catch-and-rescue.html#errors

[nelsonic]

Alternatively the more succinct and fatal:

iex> exit("Environment variables GITHUB_CLIENT_ID and GITHUB_CLIENT_SECRET undefined")
** (exit) "Environment variables GITHUB_CLIENT_ID and GITHUB_CLIENT_SECRET undefined"

I want to figure out the appropriate way of doing Logging: https://github.com/dwyl/learn-elixir/issues/149

[nelsonic]

At present the /test/elixir_auth_github_test.exs file has 28 mentions of the word "env" ... Most of the tests include some reference to the "ENVIRONMENT VARIABLES NOT SET" ... This feels unnecessarily repetitive ... 🤔

[nelsonic]

Resolved by #34 ✅