remove requirement for GOOGLE_APPLICATION_CREDENTIALS env var

README.md

@@ -16,8 +16,13 @@ $ curl https://raw.githubusercontent.com/jharshman/fwsync/master/install.sh | sh
 ## Usage
 
 ### Authentication
-Communication to the GoogleAPIs requires setting the environment variable `GOOGLE_APPLICATION_CREDENTIALS`.
-This variable should point to the path of your downloaded service account json. For example, `export GOOGLE_APPLICATION_CREDENTIALS=/Users/bob/bobserviceaccount.json`.
+Communication to the GoogleAPIs requires either setting the environment variable `GOOGLE_APPLICATION_CREDENTIALS` or
+alternatively running `gcloud auth application-default login`. If using the `GOOGLE_APPLICATION_CREDENTIALS` environment
+variable, it must point to the full path to your downloaded service account json.
+
+For example:
+
+`$ export GOOGLE_APPLICATION_CREDENTIALS=/Users/bob/bobserviceaccount.json`
 
 ### Init
 After installing, you can invoke the CLI by typing `fwsync` in your terminal.

internal/auth/auth.go

@@ -2,34 +2,30 @@ package auth
 
 import (
 	"context"
-	"errors"
-	"os"
 	"sync"
 
 	"github.com/spf13/cobra"
 	"google.golang.org/api/compute/v1"
-	"google.golang.org/api/option"
 )
 
 var (
 	GoogleCloudAuthorizedClient *compute.Service
 	once                        sync.Once
 )
 
+// Auth returns the authentication function.
 func Auth() func(cmd *cobra.Command, args []string) error {
 	return func(cmd *cobra.Command, args []string) error {
-		serviceAccountJSONPath := os.Getenv("GOOGLE_APPLICATION_CREDENTIALS")
-		if serviceAccountJSONPath == "" {
-			return errors.New("missing environment variable GOOGLE_APPLICATION_CREDENTIALS")
-		}
-		return auth(serviceAccountJSONPath)
+		return auth()
 	}
 }
 
-func auth(svcAcctFile string) (authErr error) {
+// auth will authenticate to the Google APIs using default methods.
+// https://cloud.google.com/docs/authentication/application-default-credentials#personal
+func auth() (authErr error) {
 	once.Do(func() {
 		var cc *compute.Service
-		cc, authErr = compute.NewService(context.Background(), option.WithCredentialsFile(svcAcctFile))
+		cc, authErr = compute.NewService(context.Background())
 		GoogleCloudAuthorizedClient = cc
 	})
 	return