AFAIK, URL rewrite via a git config is working for others but we need a more reliable solution for this case. It is a large majority of the users who has to maintain private packages and go get doesn't support such a common case out of the box.

URL rewrite config:

git config --global url."git@github.com:".insteadOf "https://github.com/"

I feel this is more a documentation issue rather then a problem that needs solving, I'm perfectly happy using .netrc authentication for example:
https://gist.github.com/cactus/3925422

In the case of git there seem to be plenty more solutions (which I haven't tested):
https://git-scm.com/docs/gitcredentials

Go uses different VCS and so far as I know has chosen to use HTTP(S) as it's common transport protocol. For me it would make more sense to document how each VCS would be properly configured for authentication since in the end it should be the responsibility of the VCS to authenticate.

Adding SSH as an extra transport protocol seems unnecessary complicated to combine with canonical imports and any other potential edge cases.

It uses http/s because they're most commonly left open in firewalls (from the Go FAQ, if I recall correctly). SSH is yet another common transport that any VCS could use; how they use it, I shouldn't have to care about; it should work out of the box. If I have to configure a VCS to use SSH, then in general I have to know what VCS a package is hosted with before I try to import it.

I think private Github repos work with HTTPS. The assertion above is that they only work over SSH. Can someone clarify?

They work over HTTPS by provisioning a .netrc config for example.

@rsc If private GitHub repos did work with HTTPS, then wouldn't the Go FAQ explain how to do that instead of how to do the Git URL rewrite configuration?

Change https://golang.org/cl/107775 mentions this issue: doc: update "go get" HTTPS answer to mention .netrc

I sent out a doc update in response to the comment above, and then we'll call this fixed.

golang.org/cl/107775.