Signature#SignUserId was ignoring the error returned by userIdSignatureHash. This error can happen, for example, when the Signature's Hash property is uninitialized. Not returning the error makes it hard for the user to detect the problem. Change-Id: I0ae0033e77bfb1ea1c06b0769f949e48c713adc6 Reviewed-on: https://go-review.googlesource.com/27997 Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org> Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org>