Add QR code support to nebula-cert (#297)

cmd/nebula-cert/sign.go

@@ -11,6 +11,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/skip2/go-qrcode"
 	"github.com/slackhq/nebula/cert"
 	"golang.org/x/crypto/curve25519"
 )
@@ -25,6 +26,7 @@ type signFlags struct {
 	inPubPath   *string
 	outKeyPath  *string
 	outCertPath *string
+	outQRPath   *string
 	groups      *string
 	subnets     *string
 }
@@ -40,6 +42,7 @@ func newSignFlags() *signFlags {
 	sf.inPubPath = sf.set.String("in-pub", "", "Optional (if out-key not set): path to read a previously generated public key")
 	sf.outKeyPath = sf.set.String("out-key", "", "Optional (if in-pub not set): path to write the private key to")
 	sf.outCertPath = sf.set.String("out-crt", "", "Optional: path to write the certificate to")
+	sf.outQRPath = sf.set.String("out-qr", "", "Optional: output a qr code image (png) of the certificate")
 	sf.groups = sf.set.String("groups", "", "Optional: comma separated list of groups")
 	sf.subnets = sf.set.String("subnets", "", "Optional: comma seperated list of subnet this cert can serve for")
 	return &sf
@@ -203,6 +206,18 @@ func signCert(args []string, out io.Writer, errOut io.Writer) error {
 		return fmt.Errorf("error while writing out-crt: %s", err)
 	}
 
+	if *sf.outQRPath != "" {
+		b, err = qrcode.Encode(string(b), qrcode.Medium, -5)
+		if err != nil {
+			return fmt.Errorf("error while generating qr code: %s", err)
+		}
+
+		err = ioutil.WriteFile(*sf.outQRPath, b, 0600)
+		if err != nil {
+			return fmt.Errorf("error while writing out-qr: %s", err)
+		}
+	}
+
 	return nil
 }