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

go version go1.14 linux/amd64

Does this issue reproduce with the latest release?

I believe so.

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

"linux"
"amd64"

What did you do?

I am using the acme client to perform an RFC8555 compliant workflow. The RFC specifies that NewAccount and OrderFinalization requests to respond with StatusCreated. The rfc8555.go file only accepts StatusOK responses.

A quick and easy solution would be adding StatusCreated to the following line in CreateOrderCert:
Line 295: res, err := c.post(ctx, nil, url, req, wantStatus(http.StatusOK, http.StatusCreated))

The test for this function then needs to be updated so that the /pleaseissue handler is broken up into two handlers. One for the order finalization, and one for the order polling since these two requests now expect different server responses.
Something like:

s.handle("/acme/new-account", func(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Location", s.url("/accounts/1"))
	w.WriteHeader(http.StatusCreated)
	w.Write([]byte(`{"status": "valid"}`))
})
s.handle("/pleaseissue", func(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Location", s.url("/orders/1"))
	w.WriteHeader(http.StatusCreated)
	fmt.Fprintf(w, `{"status":%q, "certificate":%q}`, StatusProcessing, s.url("/crt"))
})
s.handle("/orders/1", func(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Location", s.url("/orders/1"))
	w.WriteHeader(http.StatusOK)
	fmt.Fprintf(w, `{"status": %q, "certificate":%q}`, StatusValid, s.url("/crt"))
})
s.handle("/crt", func(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "application/pem-certificate-chain")
	pem.Encode(w, &pem.Block{Type: "CERTIFICATE", Bytes: leaf})
})