People Search and authentication

Hello,

I have a Web Application for My Sites with its My Site host Collection.
Everything is running well; users can create their personal sites without problem.

The web application for My site is using only ADFS authentication and it is not desirable to change this setting.

At this moment I dont have configurated People Search.

Here start my issue. I need to configure People Search.

I've tryed to extend My site Web application (Default zone and ADFS authentication). The extended web application is configured as NTLM authentication (Intranet zone).
After extend it, I found user profiles but, althoug a user is loged in with ADFS authentication, before show results of People Search he is asked to login again with his NTLM credentials.

My questions are:

1. Could I configure People Search only with ADFS authentication?
2. It is mandatory NTLM authentication to configure People Search?
3. In case NTLM is mandatory, how can I avoid to be asked for second time for my NTLM credentials?

Thanks!