The API and documentation for logging in with PlayFab (using an email address or user name) is messy and inconsistent.
The "Register PlayFab User" REST API documentation says "You must supply either a username or an email address"
The "Register PlayFab User" REST API documentation also says "Each account must have a unique email address in the PlayFab service."
The "Add Username Password" REST API documentation says "Each account must have a unique username and email address in the PlayFab service."
Here we have three different and contradictory statements about whether the account must have a username, email address, or both. Statements #2 and #3 are false; if you register a user with RequireBothUsernameAndEmail set to false, you can register a user that has a username but no email address.
However, although we can register a new user with just a username and no email address, we can't add a username to an anonymous account without adding an email address. Despite the endpoint's name, both username and email address are required for the "Add Username Password" endpoint.
I like the option of including a username-only registration option for players who are privacy-minded, but it's baffling that we can register an account with no email address but can't add a username to an anonymous account without adding an email address.
