The former does not make a copy of the accumulated buffer
to produce a string.

WriteByte() is faster than WriteRune() and we are not
appending non-ASCII here.

Change-Id: I562461eec2fdcf6230e46b3011fabe0979d05044
GitHub-Last-Rev: b7845f8
GitHub-Pull-Request: #785
Reviewed-on: https://go-review.googlesource.com/c/oauth2/+/694715
Reviewed-by: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Mark Freeman <markfreeman@google.com>
Reviewed-by: Sean Liao <sean@liao.dev>
Auto-Submit: Sean Liao <sean@liao.dev>

Endpoints may return errors when attempting to request device
authorization. Currently, these error codes are ignored and an
otherwise empty RetrieveError returned. This change populates
the RetrieveError similar to the oauth2 token exchange.

Fixes golang/go#75759

Change-Id: Ic00fecce290d3d3b4a40697b54ce74cc8cacab4d
GitHub-Last-Rev: 32c6ab5
GitHub-Pull-Request: #794
Reviewed-on: https://go-review.googlesource.com/c/oauth2/+/709215
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Sean Liao <sean@liao.dev>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

Change-Id: I3dd3785de7071e34320a148f35d4caa97cfd6db1
Reviewed-on: https://go-review.googlesource.com/c/oauth2/+/713361
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Sean Liao <sean@liao.dev>
Auto-Submit: Sean Liao <sean@liao.dev>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>