Fix encoding for non-ascii char in kerberos authentication

[NeffIsBack]

With the hack.lu CTF this year and therefore a swedish AD environment it was reported that Kerberos authentication does not work with special chars (e.g. öäü) that are present in some localized environments: Pennyw0rth/NetExec#963

The problem is that kerberos uses utf-8 encoding for Kerberos Strings. However, as of now both minikerberos as well as impacket both use latin1 as its encoding, resulting in failed authentication with users that contain special chars.
See:

• [MS-KILE] section 3.1.5.7
• openJDK: https://bugs.openjdk.org/browse/JDK-8200152

A PR to fix the issue in impacket has been opened: fortra/impacket#2068

With both fixes applied, pfx authentication (which uses minikerberos as well as impacket) works as intended now (Before&After):

Be aware that i have not tested the kerberos protokoll on its own with minikerberos, but i expect the same result as in impacket (failed auth for usernames with öäü etc in the name)!

[skelsec]

Be aware that i have not tested the kerberos protokoll on its own with minikerberos,
YOLO