Copied from the old forum:
Every time I register same user to jawbone for allowing me to retrieve data, it is returning same refresh token. If that is always true Can I use refresh token to update user details in my application. As there is not EncodedUserId come in response by which I can identify user.
The refresh token is not guaranteed to be the same forever, so you should not make that assumption.
Additionally, the refresh token can only be used to get new access tokens and not to retrieve any other data.
If you are looking for a unique ID to represent an UP user, you should use the xid retrieved from the User endpoint.
The user's xid is also returned as the user_xid in the meta section of any UP API response.