@venkat have you looked at the session sharing plugin?
https://github.com/julianlam/nodebb-plugin-session-sharing
It provide functions for retrieving the NodeBB id from your id.
Using that plugin is the recommended way of sharing sessions between applications.
Changing the NodeBB id format is a futile effort. You can't just change it to a string. The closest you can do is map your id to the NodeBB id.