Add a way for cronjobs to automatically renew certificates.

cli.go

@@ -47,6 +47,13 @@ func main() {
 			Name:   "renew",
 			Usage:  "Renew a certificate",
 			Action: renew,
+			Flags: []cli.Flag{
+				cli.IntFlag{
+					Name: "days",
+					Value: 0,
+					Usage: "The number of days left on a certificate to renew it.",
+				},
+			},
 		},
 	}
 

cli_handlers.go

@@ -7,6 +7,7 @@ import (
 	"os"
 	"path"
 	"strings"
+	"time"
 
 	"github.com/codegangsta/cli"
 	"github.com/xenolf/lego/acme"
@@ -181,6 +182,17 @@ func renew(c *cli.Context) {
 			return
 		}
 
+		if c.IsSet("days") {
+			expTime, err := acme.GetPEMCertExpiration(certBytes)
+			if err != nil {
+				logger().Printf("Could not get Certification expiration for domain %s", domain)
+			}
+
+			if int(expTime.Sub(time.Now()).Hours() / 24.0) <= c.Int("days") {
+				continue;
+			}
+		}
+
 		keyBytes, err := ioutil.ReadFile(privPath)
 		if err != nil {
 			logger().Printf("Error while loading the private key for domain %s\n\t%v", domain, err)