I have four guesses so far:


  none, "on", "for", and "by".



Question: Salesforce Mobile SDK Community Registration
Answer: This link provides all configuration items that you need to have in place to use Communities with the Salesforce Mobile SDK. Depending on the kind of user license, you also need to have appropriate permissions (such as API enabled for Portal users) - refer this link.


SDK does not provide any explicit support for self-registration.