login method
Set the current user from a given user object.
The object is expected to contain at least the id key.
The user object will be stored in the _user map with the key being the
current guard.
Returns the current instance of the Auth class.
Implementation
Auth login(Map<String, dynamic> user, [bool basic = false]) {
_user[_userGuard] = user;
if (basic) {
_updateSession();
}
return this;
}