instance method signer

# File activestorage/lib/active_storage/service/gcs_service.rb, line 220
      def signer
        # https://googleapis.dev/ruby/google-cloud-storage/latest/Google/Cloud/Storage/Project.html#signed_url-instance_method
        lambda do |string_to_sign|
          iam_client = Google::Apis::IamcredentialsV1::IAMCredentialsService.new

          scopes = ["https://www.googleapis.com/auth/iam"]
          iam_client.authorization = Google::Auth.get_application_default(scopes)

          request = Google::Apis::IamcredentialsV1::SignBlobRequest.new(
            payload: string_to_sign
          )
          resource = "projects/-/serviceAccounts/#{issuer}"
          response = iam_client.sign_service_account_blob(resource, request)
          response.signed_blob
        end
      end