SPN discovery gets wrong service when it does not first attempt accessing the SPN for the given hostname rather than immediately doing a reverse lookup.

[AJH16]

I was working through an issue in GitLFS that traced down to an apparently errant behavior in spnego. On Windows, in the spnego_windows.go file, the SetSPNEGOHeader attempts to form a Canonicalized hostname from the given URL's hostname without ever trying the given host. In any environment with multiple services on a given IP, this could result in an incorrect SPN being chosen. This canonicalization is a good attempt at recovering from an SPN missing for a service, but causes intermittent incorrect SPN selection when the given host is valid and multiple hosts share an IP address.

[AJH16]

Note for anyone dealing with this problem. You can locally fix it using your hosts file if you only need to manage to connect to one particular SPN on that machine. If you have multiple records for a given IP in the hosts file, spnego will select the first listed hostname for the service to use as the HTTP/hostname SPN.