I've forked and added more functionality to the ebayapi gem

If you want to create multi-user eBay apps, you'll need the ebayapi trading API XML gem created by Cody Fauser to let you:

  1. Get a session id (the existing version does not conform to the correct GetSessionID, passing XMLRequesterCredentials node instead of the specified one that passes DevID, AppID and AuthCert.
  2. Pass an RuName for your app from the config

The existing gem doesn't support these, but I've added it today. I'll probably post again soon about how to set up multi-user tokens as mentioned here using the updated ebayapi gem.

Here's the updated ebayapi gem on github. To install it on your machine, you can run:
views