Add ADC support (#532)

* Add ADC support

Change-Id: I30498dc41703428ee179c104d783e19bb12abb69

* Reorder configs to keep service account fields together

Change-Id: Ic55dfa9d3a45b8bef88ab38d34d278d21f8b1757

* Rename env variable

Change-Id: I5b3aea4c0da6be73884a532145ea879b8bfba4f3

* Prioritize the use_application_default_credentials flag

Change-Id: I2eed7176be117abbd47be64871cda3e69636061e

Author: dorasun

Gemfile

@@ -13,3 +13,4 @@ gem 'yard', '~> 0.9.27'
 gem 'rubocop', require: false
 gem 'rubocop-google_ads', require: false
 gem 'grpc', ['~> 1.0', '!= 1.74.0']
+gem 'googleauth', '~> 1.15.1'

google_ads_config.rb

@@ -26,6 +26,11 @@
   c.client_secret = 'INSERT_CLIENT_SECRET_HERE'
   c.refresh_token = 'INSERT_REFRESH_TOKEN_HERE'
 
+  # You can also authenticate using Application Default Credentials (ADC)
+  # To understand how ADC discovers credentials in a given environment,
+  # see: https://developers.google.com/identity/protocols/application-default-credentials.
+  c.use_application_default_credentials = false
+
   # Whether to use the Google Cloud Organization of your Google Cloud
   # project instead of developer token to determine your Google Ads API access levels.
   # Use this flag only if you are enrolled into a limited pilot that supports

lib/google/ads/google_ads/config.rb

@@ -27,6 +27,7 @@ class Config
         attr_accessor :client_secret
         attr_accessor :keyfile
         attr_accessor :impersonate
+        attr_accessor :use_application_default_credentials
         attr_accessor :authentication
 
         attr_accessor :developer_token
@@ -51,6 +52,7 @@ def initialize(&block)
           @client_secret = nil
           @keyfile = nil
           @impersonate = nil
+          @use_application_default_credentials = nil
           @authentication = nil
 
           @developer_token = nil

lib/google/ads/google_ads/google_ads_client.rb

@@ -35,6 +35,7 @@
 require 'json'
 require 'openssl'
 require 'signet/oauth_2/client'
+require 'googleauth'
 require 'delegate'
 
 module Google
@@ -100,6 +101,7 @@ def load_environment_config
           @config.client_secret = ENV.fetch("GOOGLE_ADS_CLIENT_SECRET", @config.client_secret)
           @config.keyfile = ENV.fetch("GOOGLE_ADS_JSON_KEY_FILE_PATH", @config.keyfile)
           @config.impersonate = ENV.fetch("GOOGLE_ADS_IMPERSONATED_EMAIL", @config.impersonate)
+          @config.use_application_default_credentials = ENV.fetch("GOOGLE_ADS_USE_APPLICATION_DEFAULT_CREDENTIALS", @config.use_application_default_credentials)
           @config.developer_token = ENV.fetch("GOOGLE_ADS_DEVELOPER_TOKEN", @config.developer_token)
           @config.login_customer_id = ENV.fetch("GOOGLE_ADS_LOGIN_CUSTOMER_ID", @config.login_customer_id)
           @config.linked_customer_id = ENV.fetch("GOOGLE_ADS_LINKED_CUSTOMER_ID", @config.linked_customer_id)
@@ -201,7 +203,9 @@ def decode_warning(warning)
         private
 
         def get_credentials
-          if @config.authentication
+          if @config.use_application_default_credentials
+            get_application_default_credentials
+          elsif @config.authentication
             @config.authentication
           elsif @config.keyfile
             get_service_account_credentials
@@ -236,6 +240,12 @@ def get_service_account_credentials
             scope: [SCOPE],
           ).updater_proc
         end
+        
+        # Provides a Google::Auth::Credentials initialized with Application
+        # Default Credentials specified in the config.
+        def get_application_default_credentials
+          Google::Auth.get_application_default(SCOPE).updater_proc
+        end
 
         # Create the default logger, useful if the user hasn't defined one.
         def create_default_logger()