x/crypto/acme: support subproblems

[mbaynton]

What version of Go are you using (go version)?

$ go version
go version go1.13 linux/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/mpantheon/.cache/go-build"
GOENV="/home/mpantheon/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/mpantheon/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build487582068=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Called AuthorizeOrder to request a new ACMEv2 Order with identifiers rejected by the CA

What did you expect to see?

An acme.Error populated with RFC 8555 subproblems

What did you see instead?

An acme.Error with no subproblems available.

This limits the information clients can provide to users and prevents automated corrections to the invalid Order, such as by removing the the rejected identifiers and requesting a new Order.

[gopherbot]

Change https://golang.org/cl/233165 mentions this issue: x/crypto/acme: add support for subproblems

[toothrot]

/cc @FiloSottile @x1ddos

[rolandshoemaker]

Since this changes an API, marking it as a proposal.

CL 233165 proposes the following API addition/change:

type Subproblem struct {
	Type        string
	Detail      string
	Instance    string
	Identifier  *AuthzID
}

func (sp Subproblem) String() string

type Error struct {
	...
	Subproblems []Subproblem
}

[rsc]

Based on the discussion above, this proposal seems like a likely accept.
— rsc for the proposal review group

[rsc]

No change in consensus, so accepted. 🎉
This issue now tracks the work of implementing the proposal.
— rsc for the proposal review group