GCE setup tool: more graceful OAuth setup

Change-Id: I28893735c49da18d3890a0df07b071048c29ba68

misc/gce/.gitignore

@@ -1,3 +1,3 @@
 client-id.dat
 client-secret.dat
-auth-code.dat
+token.dat

misc/gce/create.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"bufio"
 	"flag"
 	"io/ioutil"
 	"log"
@@ -26,6 +27,8 @@ func readFile(v string) string {
 }
 
 var config = &oauth.Config{
+	// The client-id and secret should be for an "Installed Application" when using
+	// the CLI. Later we'll use a web application with a callback.
 	ClientId:     readFile("client-id.dat"),
 	ClientSecret: readFile("client-secret.dat"),
 	Scope: strings.Join([]string{
@@ -49,19 +52,26 @@ func main() {
 	imageURL := "https://www.googleapis.com/compute/v1/projects/coreos-cloud/global/images/coreos-alpha-402-2-0-v20140807"
 	machType := prefix + "/zones/" + *zoneFlag + "/machineTypes/" + *machFlag
 
-	if _, err := os.Stat("auth-code.dat"); err != nil {
-		log.Printf("No auth code in file auth-code.dat. Get auth code from %v", config.AuthCodeURL("my-state"))
-		return
-	}
-	authCode := readFile("auth-code.dat")
-
 	tr := &oauth.Transport{
 		Config: config,
 	}
-	t, err := tr.Exchange(authCode)
+
+	tokenCache := oauth.CacheFile("token.dat")
+	token, err := tokenCache.Token()
 	if err != nil {
-		log.Fatal(err)
+		log.Printf("Error getting token from %s: %v", string(tokenCache), err)
+		log.Printf("Get auth code from %v", config.AuthCodeURL("my-state"))
+		os.Stdout.Write([]byte("\nEnter auth code: "))
+		sc := bufio.NewScanner(os.Stdin)
+		sc.Scan()
+		authCode := strings.TrimSpace(sc.Text())
+		token, err = tr.Exchange(authCode)
+		if err != nil {
+			log.Fatalf("Error exchanging auth code for a token: %v", err)
+		}
+		tokenCache.PutToken(token)
 	}
-	log.Printf("Got token: %#v", t)
+
+	log.Printf("Got token: %#v", token)
 	_, _ = machType, imageURL
 }