oscarolbe / goth

Elixir package for Oauth authentication via Google Cloud APIs

Goth

Google + Auth = Goth

A simple library to generate and retrieve OAuth2 tokens for use with Google Cloud Service accounts.

It can either retrieve tokens using service account credentials or from Google's metadata service for applications running on Google Cloud Platform.

Installation

1. Add Goth to your list of dependencies in mix.exs:

def deps do
  [{:goth, "~> 0.8.0"}]
end

2. Pass in your credentials json downloaded from your GCE account:

config :goth,
  json: "path/to/google/json/creds.json" |> File.read!

Or, via an ENV var:

config :goth, json: {:system, "GCP_CREDENTIALS"}

Or, via your own config module:

config :goth, config_module: MyConfigMod

defmodule MyConfigMod do
  use Goth.Config
  
  def init(config) do
    {:ok, Keyword.put(config, :json, System.get_env("MY_GCP_JSON_CREDENTIALS"))}
  end
end

You can skip the last step if your application will run on a GCP or GKE instance with appropriate permissions.

If you need to set the email account to impersonate. For example when using service accounts

config :goth,
  json: {:system, "GCP_CREDENTIALS"},
  actor_email: "[email protected]"

Alternatively, you can pass your sub email on a per-call basis, for example:

Goth.Token.for_scope("https://www.googleapis.com/auth/pubsub", 
                     "[email protected]")

Usage

Retrieve a token:

Call Token.for_scope/1 passing in a string of scopes, separated by a space:

alias Goth.Token
{:ok, token} = Token.for_scope("https://www.googleapis.com/auth/pubsub")
#=>
  %Goth.Token{
    expires: 1453356568,
    token: "ya29.cALlJ4ICWRvMkYB-WsAR-CZnExE459PA7QPqKg5nei9y2T9-iqmbcgxq8XrTATNn_BPim",
    type: "Bearer"
  }