If email and private key is not provided, try to retrieve token from the GCE metaserver. Fixes #3.

Author: rakyll

lib/common/connection.js

@@ -18,6 +18,8 @@ var GAPIToken = require('gapitoken'),
   async = require('async'),
   req = require('request');
 
+var metadataTokenUrl = 'http://metadata/computeMetadata/v1/instance/service-accounts/default/token';
+
 /**
  * Token represents an access token
  * @param {string} accessToken  Access token.
@@ -80,6 +82,26 @@ Connection.prototype.connect = function(callback) {
  */
 Connection.prototype.fetchToken = function(callback) {
   var that = this;
+  if (!this.email || !this.privateKey) {
+    // We should be on GCE, try to retrieve token from
+    // the metadata from server.
+    req({
+      method: 'get',
+      uri: metadataTokenUrl,
+      headers: {
+        'X-Google-Metadata-Request': 'True'
+      },
+      json: true
+    }, function(err, res, body) {
+      if (err || !body.access_token) {
+        // TODO: Provide better context about the error here.
+        return callback(err);
+      }
+      var exp = new Date(body.token_expires * 1000);
+      callback(null, new Token(body.access_token, exp));
+    });
+    return;
+  }
   var gapi = new GAPIToken({
     iss: this.email,
     keyFile: this.privateKey,