Fix goth config

Author: ericmj

config/dev.exs

@@ -70,5 +70,3 @@ config :phoenix, :plug_init_mode, :runtime
 config :diff,
   tmp_dir: Path.expand("tmp/dev"),
   storage_impl: Diff.Storage.Local
-
-config :goth, config: %{"project_id" => "diff"}

config/runtime.exs

@@ -12,8 +12,6 @@ if config_env() == :prod do
     url: [host: System.fetch_env!("DIFF_HOST")],
     secret_key_base: System.fetch_env!("DIFF_SECRET_KEY_BASE")
 
-  config :goth, json: System.fetch_env!("DIFF_GCP_CREDENTIALS")
-
   config :sentry,
     dsn: System.fetch_env!("DIFF_SENTRY_DSN"),
     environment_name: System.fetch_env!("DIFF_ENV")

config/test.exs

@@ -6,8 +6,6 @@ config :diff, DiffWeb.Endpoint,
   http: [port: 5004],
   server: false
 
-config :goth, config: %{"project_id" => "diff"}
-
 # Print only warnings and errors during test
 config :logger, level: :warning
 

lib/diff/application.ex

@@ -10,6 +10,7 @@ defmodule Diff.Application do
 
     # List all child processes to be supervised
     children = [
+      goth_spec(),
       {Task.Supervisor, name: Diff.Tasks},
       # Start the PubSub system
       {Phoenix.PubSub, name: Diff.PubSub},
@@ -32,4 +33,20 @@ defmodule Diff.Application do
     DiffWeb.Endpoint.config_change(changed, removed)
     :ok
   end
+
+  if Mix.env() == :prod do
+    defp goth_spec() do
+      credentials =
+        "DIFF_GCP_CREDENTIALS"
+        |> System.fetch_env!()
+        |> Jason.decode!()
+
+      options = [scope: "https://www.googleapis.com/auth/devstorage.read_write"]
+      {Goth, name: Diff.Goth, source: {:service_account, credentials, options}}
+    end
+  else
+    defp goth_spec() do
+      {Task, fn -> :ok end}
+    end
+  end
 end

lib/diff/storage/gcs.ex

@@ -4,7 +4,6 @@ defmodule Diff.Storage.GCS do
   @behaviour Diff.Storage
 
   @gs_xml_url "https://storage.googleapis.com"
-  @oauth_scope "https://www.googleapis.com/auth/devstorage.read_write"
 
   def get(package, from_version, to_version) do
     with {:ok, hash} <- combined_checksum(package, from_version, to_version),
@@ -44,7 +43,7 @@ defmodule Diff.Storage.GCS do
   end
 
   defp headers() do
-    token = Goth.fetch!(@oauth_scope)
+    token = Goth.fetch!(Diff.Goth)
     [{"authorization", "#{token.type} #{token.token}"}]
   end