LF_Mcxixif_ it's something along these lines:
POST /api/users
{
"data": {
"attributes:" {
"username": "username",
"email": "email",
"password": "password"
}
}
}
Password change can only be done if the request is made with an admin access token, otherwise normal users can only request a password change by email.
That's not possible with native REST API. Absolute URLs as avatars can only be set via the database directly. You'll need to use the Extension API to allow setting URLs via the REST API.