In my iOS application on the initial launch user can sign in with 3 different ways: email/pass, Facebook or Twitter. Registering with each of them will cause to create 3 different users.
Later in my app user should have the possibility to link accounts. For example, if he signed in with email/pass, then he should be able to link Facebook and Twitter. 

Parse native -linkInBackground works great in case we have only one user, which is email/pass. But if we will already have Facebook or Twitter account created, the Parse SDK will reply with error, saying that this account is already linked to the social.
At first I thought that I've figured out the workaround: 

1. Save the old user data
2. Delete the old user
3. Sign in (not link) with the social (say, Facebook)
4. Fill all the data from the saved user to the new one.

Everything went well with one social, but it appeared that the "authData" field, which is very important in my approach, is not contained in the [PFUser currentUser]. And so despite the fact that all other data is transferred successfully, the authData is not transferred, so that we don't have authentication data of the old user.

The question is: Is there a way to get authData from Parse, or is there any "legal" way to achieve my initial goal of merging (linking) two (three) users?