Update dependencies/vendor (#1659)

vendor/golang.org/x/crypto/acme/acme.go

@@ -4,7 +4,7 @@
 
 // Package acme provides an implementation of the
 // Automatic Certificate Management Environment (ACME) spec.
-// The intial implementation was based on ACME draft-02 and
+// The initial implementation was based on ACME draft-02 and
 // is now being extended to comply with RFC 8555.
 // See https://tools.ietf.org/html/draft-ietf-acme-acme-02
 // and https://tools.ietf.org/html/rfc8555 for details.

vendor/golang.org/x/crypto/acme/rfc8555.go

@@ -410,3 +410,29 @@ func isAlreadyRevoked(err error) bool {
 	e, ok := err.(*Error)
 	return ok && e.ProblemType == "urn:ietf:params:acme:error:alreadyRevoked"
 }
+
+// ListCertAlternates retrieves any alternate certificate chain URLs for the
+// given certificate chain URL. These alternate URLs can be passed to FetchCert
+// in order to retrieve the alternate certificate chains.
+//
+// If there are no alternate issuer certificate chains, a nil slice will be
+// returned.
+func (c *Client) ListCertAlternates(ctx context.Context, url string) ([]string, error) {
+	if _, err := c.Discover(ctx); err != nil { // required by c.accountKID
+		return nil, err
+	}
+
+	res, err := c.postAsGet(ctx, url, wantStatus(http.StatusOK))
+	if err != nil {
+		return nil, err
+	}
+	defer res.Body.Close()
+
+	// We don't need the body but we need to discard it so we don't end up
+	// preventing keep-alive
+	if _, err := io.Copy(ioutil.Discard, res.Body); err != nil {
+		return nil, fmt.Errorf("acme: cert alternates response stream: %v", err)
+	}
+	alts := linkHeader(res.Header, "alternate")
+	return alts, nil
+}