Mark auth classes as deprecated

lib/google/api_client/auth/installed_app.rb

@@ -33,6 +33,7 @@ module Google
     #    drive = Drive::DriveService.new
     #    drive.authorization = authorization
     #
+    # @deprecated Use google-auth-library-ruby instead
     class InstalledAppFlow
 
       RESPONSE_BODY = <<-HTML

lib/google/api_client/auth/key_utils.rb

@@ -18,6 +18,7 @@ module Google
     # Helper for loading keys from the PKCS12 files downloaded when
     # setting up service accounts at the APIs Console.
     #
+    # @deprecated Use google-auth-library-ruby instead
     module KeyUtils
       ##
       # Loads a key from PKCS12 file, assuming a single private key

lib/google/api_client/auth/storage.rb

@@ -21,6 +21,7 @@ module Google
     # JSON serialized file. Meant to resemble the serialized format
     # http://google-api-python-client.googlecode.com/hg/docs/epy/oauth2client.file.Storage-class.html
     #
+    # @deprecated Use google-auth-library-ruby instead
     class Storage
 
       AUTHORIZATION_URI = 'https://accounts.google.com/o/oauth2/auth'

lib/google/api_client/auth/storages/file_store.rb

@@ -21,6 +21,7 @@ module Google
     # JSON serialized file. Meant to resemble the serialized format
     # http://google-api-python-client.googlecode.com/hg/docs/epy/oauth2client.file.Storage-class.html
     #
+    # @deprecated Use google-auth-library-ruby instead
     class FileStore
 
       attr_accessor :path

lib/google/api_client/auth/storages/redis_store.rb

@@ -16,6 +16,7 @@ require 'json'
 
 module Google
   class APIClient
+    # @deprecated Use google-auth-library-ruby instead
     class RedisStore
 
       DEFAULT_REDIS_CREDENTIALS_KEY = "google_api_credentials"

lib/google/api_client/client_secrets.rb

@@ -23,7 +23,7 @@ module Google
     # inspired by the Google API Python client.
     #
     # @see https://developers.google.com/api-client-library/python/guide/aaa_client_secrets
-    #
+    # @deprecated Use google-auth-library-ruby instead
     # @example
     #   {
     #     "web": {