maybe I’m searching wrong, but I couldn’t get a valid answer regarding the following topic since yet.
The current REST entry point for the user picker currently supports the (deprecated) user key as a valid input in the query parameter. With the upcoming GDPR changed, this key will be removed and replaced through the account id, which is already defined in the response of this entry point.
while being able to search for all the stuff (name, mail address, and userkey), I’m unable to search for an existing account id. For preselecting user picker fields, it would be cool, if the entry point could support the account id as valid input for the query parameter.