Updated request.GetAuthType to handle multi-value auth headers

[VladimirKhvostov]

GetAuthType method in https://github.com/github/git-lfs/blob/master/httputil/request.go#L174 only takes first WWW-Authenticate header into account. If server sends the following headers:

WWW-Authenticate: Bearer
WWW-Authenticate: Negotiate
WWW-Authenticate: NTLM

the code returns "basic", which is definitely not correct in this case.

This change fixes this issue. With this change we will also handle Negotiate authentication.

Bug: #1377

[ttaylorr]

The inner contents of this loop look good. I wonder if we could make things a little bit clearer by making removing the WwwAuthenticateHeader and LfsAuthenticateHeader consts in favor of a single:

var (
        AuthenticateHeaders = []string{"Www-Authenticate", "Lfs-Authenticate"}
)

since we never use them individually, only in this form on line 184.

[VladimirKhvostov]

I agree. I was thinking about this, but was not sure what is the right way to do this in GO lang. Thanks for teaching me best practices.

[ttaylorr]

Thanks for re-opening this PR 😄 . Few more comments from me, but this looks great!

Like I said, feel free to not go with my test-case suggestion. I'd be fine merging this in either way.

[ttaylorr]

Great, thanks! 👍

[technoweenie]

Thanks for the patch! I made a few changes in 29e8876 so that the httputil package doesn't export values like BasicAuthType or AuthenticateHeaders. Those are only used for the internals of the httputil package, so they don't need to be exported.