Attributes - how to specify/require/query them?

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1. I can't find how to specify in metadata.xml what attributes my SP requires from IdP.

   When I add my SP metadata xml to my https://samlidp.io/ IdP, I get this message

   

   It works only when email switch is ON, otherwise I get null in

   // UserCreatorInterface
   $this->usernameMapper->getUsername($response)

2. How to make AttributeQuery? As I understand this is not implemented?

   On user login (on AuthnRequest Response) I want to make an AttributeQuery and abort login process if IdP doesn't provide the required attributes (for example email, First Name, Last Name).

P.S. This bundle is a big machinery for me, so sorry if this question is too obvious for you. I have spent almost a week inspecting it and still no clear vision about its internals.