User documents have ids when onCreateUser and validateNewUser hooks run

packages/accounts-base/accounts_server.js

@@ -122,9 +122,19 @@
     return user;
   };
   Accounts.insertUserDoc = function (options, user) {
-    // add created at timestamp (and protect passed in user object from
-    // modification)
-    user = _.extend({createdAt: +(new Date)}, user);
+    // - clone user document, to protect from modification
+    // - add createdAt timestamp
+    // - prepare an _id, so that you can modify other collections (eg
+    // create a first task for every new user)
+    //
+    // XXX If the onCreateUser or validateNewUser hooks fail, we might
+    // end up having modified some other collection
+    // inappropriately. The solution is probably to have onCreateUser
+    // accept two callbacks - one that gets called before inserting
+    // the user document (in which you can modify its contents), and
+    // one that gets called after (in which you should change other
+    // collections)
+    user = _.extend({createdAt: +(new Date), _id: Random.id()}, user);
 
     var result = {};
     if (options.generateLoginToken) {

packages/accounts-base/accounts_tests.js

@@ -7,6 +7,14 @@ Tinytest.add('accounts - config validates keys', function (test) {
   });
 });
 
+Tinytest.add('accounts - validateNewUser gets passed user with _id', function (test) {
+  Accounts.validateNewUser(function (user) {
+    test.equal(typeof user._id, "string");
+    return true;
+  });
+  Accounts.updateOrCreateUserFromExternalService('foobook', {id: Random.id()});
+});
+
 Tinytest.add('accounts - updateOrCreateUserFromExternalService - Facebook', function (test) {
   var facebookId = Random.id();