You can't use the encode function, nor connect to steemconnect with your private memo key. I wanted this application to be used only with the private memo key, because :

  • there was no real usage of it (until now with Steem Messenger);
  • a chat application doesn't require to be able to make transfers, vote, post, and so on;
  • this is the safest way to verify your authority as their is no critical issue associated with those keys. The only thing you can do with this key is encode/decode memos.

Hmmm Interesting. I may fork your code and try implement it on my app :)