will query the DNS for
           _kerberos._tcp.dc._msdcs.domain.local).
:param key: (optional) pass the Key object.
:param password: (optional) otherwise, pass the user's password
:param realm: (optional) the realm to use. Otherwise use the one from UPN.
:param host: (optional) the host performing the AS-Req. WIN10 by default.

:return: returns a named tuple (asrep=<...>, sessionkey=<...>)

Example::

    >>> # The KDC is on 192.168.122.17, we ask a TGT for user1
    >>> krb_as_req("user1@DOMAIN.LOCAL", "192.168.122.17", password="Password1")

Equivalent::

    >>> from scapy.libs.rfc3961 import Key, EncryptionType
    >>> key = Key(EncryptionType.AES256_CTS_HMAC_SHA1_96, key=hex_bytes("6d0748c546
    ...: f4e99205e78f8da7681d4ec5520ae4815543720c2a647c1ae814c9"))
    >>> krb_as_req("user1@DOMAIN.LOCAL", "192.168.122.17", key=key)
r