Add fog deprecation warning

lib/cloud_controller/blobstore/client_provider.rb

@@ -20,6 +20,12 @@ def self.provide(options:, directory_key:, root_dir: nil, resource_type: nil)
         when 'storage-cli'
           provide_storage_cli(options, directory_key, root_dir, resource_type)
         when 'fog', nil, ''
+          Steno.logger('cc.blobstore').warn(
+            'blobstore.fog-deprecated',
+            message: "[DEPRECATION WARNING] The fog blobstore client is DEPRECATED and will be REMOVED. " \
+              "Please migrate to blobstore_type 'storage-cli' as soon as possible. " \
+              "See https://github.com/cloudfoundry/community/blob/main/toc/rfc/rfc-0043-cc-blobstore-storage-cli.md for details."
+          )
           provide_fog(options, directory_key, root_dir)
         else
           provide_webdav(options, directory_key, root_dir)

spec/unit/lib/cloud_controller/blobstore/client_provider_spec.rb

@@ -32,6 +32,15 @@ module Blobstore
           expect(FogClient).to have_received(:new)
         end
 
+        it 'logs a deprecation warning' do
+          logger = instance_double(Steno::Logger, warn: nil)
+          allow(Steno).to receive(:logger).with('cc.blobstore').and_return(logger)
+
+          ClientProvider.provide(options: options, directory_key: 'key')
+
+          expect(logger).to have_received(:warn).with('blobstore.fog-deprecated', hash_including(:message))
+        end
+
         context 'when an aws encryption option is requested' do
           before do
             options.merge!(fog_aws_storage_options: { encryption: 'my organic algo' })