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Implement DNS hostname canonicalization #50

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steelman wants to merge 1 commit into pythongssapi:main from steelman:dns-canonicalize-hostname

Commits on Apr 12, 2024

Implement DNS hostname canonicalization

Optionally resolve hostname via CNAME recrord to its canonical form
(A or AAAA record). Optionally use reverse DNS query.

Such code is necessary on Windows platforms where SSPI (unlike MIT
Kerberos[1]) does not implement such operation and it is applications'
responsibility[2] to take care of CNAME resolution. However, the code
seems universal enough to put it into the library rather than in every
single program using requests_gssapi.

Warning: Usage of insecure DNS queries is explicitly forbidden in
RFC 4120[3] and may result in the risk of man-in-the-middle attack.

[1] https://github.com/krb5/krb5/blob/ec71ac1cabbb3926f8ffaf71e1ad007e4e56e0e5/src/lib/krb5/os/sn2princ.c#L99
[2] https://learn.microsoft.com/en-us/previous-versions/office/sharepoint-server-2010/gg502606(v=office.14)?redirectedfrom=MSDN#kerberos-authentication-and-dns-cnames
[3] https://datatracker.ietf.org/doc/html/rfc4120

steelman committed Apr 12, 2024