docs: Add warning to deprecated credential flow

google-apis-core/lib/google/api_client/auth/storage.rb

@@ -38,6 +38,11 @@ class Storage
       #
       # @param [Object] store
       #  Storage object
+      #
+      # @note Warning: This class is part of a deprecated credentials flow.
+      #   Providing an unvalidated credential configuration to Google APIs can
+      #   compromise the security of your systems and data. Use
+      #   google-auth-library-ruby instead.
       def initialize(store)
         @store= store
         @authorization = nil

google-apis-core/lib/google/api_client/auth/storages/file_store.rb

@@ -37,6 +37,11 @@ def initialize(path)
 
       ##
       # Attempt to read in credentials from the specified file.
+      #
+      # @note Warning: This method is part of a deprecated credentials flow.
+      #   Providing an unvalidated credential configuration to Google APIs can
+      #   compromise the security of your systems and data. Use
+      #   google-auth-library-ruby instead.
       def load_credentials
         open(path, 'r') { |f| JSON.parse(f.read) }
       rescue

google-apis-core/lib/google/api_client/auth/storages/redis_store.rb

@@ -37,6 +37,12 @@ def initialize(redis, key = nil)
 
       ##
       # Attempt to read in credentials from redis.
+      #
+      # @note Warning: This method is part of a deprecated credentials flow.
+      #   Providing an unvalidated credential configuration to Google APIs can
+      #   compromise the security of your systems and data. Use
+      #   google-auth-library-ruby instead.
+      #
       # @return [Hash]
       def load_credentials
         credentials = redis.get redis_credentials_key