Add support for negotiate auth in Git LFS

Summary

Git LFS currently supports basic auth and NTLM with SSPI. However, there is no support for negotiate auth (Kerberos ticket-based authentication).

This feature request is based on a customer's request and is quoted here:

I'm pretty sure Basic auth does work for LFS for us. I can use my username and password with LFS tasks. The issue is, the majority of our users don't have usernames and passwords. They use SSO with government PIV cards. That is why we need LFS to use negotiate, so they can authenticate.

Workarounds

1. Switch to basic auth
2. Use NTML with SSPI