fix problem with temporal credenntials

lib/google-wedoops/authenticator.rb

@@ -59,9 +59,17 @@ module Wedoops
                         json_key_io: File.open(@credentials_file_path),
                         scope: @scopes)
                 else
+                    file = Tempfile.new(user_id)
+                    begin
+                    file.write(@credentials_json)
                     @credentials = ::Google::Auth::ServiceAccountCredentials.make_creds(
-                        json_key_io: @credentials_json,
+                        json_key_io: File.open(file),
                         scope: @scopes)
+                    ensure
+                    file.close
+                    file.unlink   # deletes the temp file
+                    end
+                   
                 end
                 
                 @credentials.sub = user_id