how SameSite attribute added to my Asp.net_SessionID cookie automatically?

Add these options to web.config for sameSite=None , Lax or Strict

<system.web>
    <httpCookies sameSite="None"/>
    <sessionState cookieSameSite="None" />
    <authentication mode="Forms">
        <forms cookieSameSite="None" />
    </authentication>