all: fix printf(var) mistakes detected by latest printf checker

These were problematic but previously easy to miss. They're now
easy to spot thanks to build failures at Go tip as of CL 610736.

For golang/go#68796.

Change-Id: I167f2cce2376b4070460389c673d973e4521d3dc
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/610797
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Alan Donovan <adonovan@google.com>

acme/autocert/internal/acmetest/ca.go

@@ -308,7 +308,7 @@ func (ca *CAServer) handle(w http.ResponseWriter, r *http.Request) {
 		}
 
 		if err := decodePayload(&req, r.Body); err != nil {
-			ca.httpErrorf(w, http.StatusBadRequest, err.Error())
+			ca.httpErrorf(w, http.StatusBadRequest, "%v", err)
 			return
 		}
 
@@ -328,7 +328,7 @@ func (ca *CAServer) handle(w http.ResponseWriter, r *http.Request) {
 			Identifiers []struct{ Value string }
 		}
 		if err := decodePayload(&req, r.Body); err != nil {
-			ca.httpErrorf(w, http.StatusBadRequest, err.Error())
+			ca.httpErrorf(w, http.StatusBadRequest, "%v", err)
 			return
 		}
 		ca.mu.Lock()
@@ -352,7 +352,7 @@ func (ca *CAServer) handle(w http.ResponseWriter, r *http.Request) {
 		defer ca.mu.Unlock()
 		o, err := ca.storedOrder(strings.TrimPrefix(r.URL.Path, "/orders/"))
 		if err != nil {
-			ca.httpErrorf(w, http.StatusBadRequest, err.Error())
+			ca.httpErrorf(w, http.StatusBadRequest, "%v", err)
 			return
 		}
 		if err := json.NewEncoder(w).Encode(o); err != nil {
@@ -412,7 +412,7 @@ func (ca *CAServer) handle(w http.ResponseWriter, r *http.Request) {
 		orderID := strings.TrimPrefix(r.URL.Path, "/new-cert/")
 		o, err := ca.storedOrder(orderID)
 		if err != nil {
-			ca.httpErrorf(w, http.StatusBadRequest, err.Error())
+			ca.httpErrorf(w, http.StatusBadRequest, "%v", err)
 			return
 		}
 		if o.Status != acme.StatusReady {
@@ -427,7 +427,7 @@ func (ca *CAServer) handle(w http.ResponseWriter, r *http.Request) {
 		b, _ := base64.RawURLEncoding.DecodeString(req.CSR)
 		csr, err := x509.ParseCertificateRequest(b)
 		if err != nil {
-			ca.httpErrorf(w, http.StatusBadRequest, err.Error())
+			ca.httpErrorf(w, http.StatusBadRequest, "%v", err)
 			return
 		}
 		// Issue the certificate.
@@ -449,7 +449,7 @@ func (ca *CAServer) handle(w http.ResponseWriter, r *http.Request) {
 		defer ca.mu.Unlock()
 		o, err := ca.storedOrder(strings.TrimPrefix(r.URL.Path, "/issued-cert/"))
 		if err != nil {
-			ca.httpErrorf(w, http.StatusBadRequest, err.Error())
+			ca.httpErrorf(w, http.StatusBadRequest, "%v", err)
 			return
 		}
 		if o.Status != acme.StatusValid {