create new users on account's shard

closes #CORE-901

Change-Id: I3bc1ac9bd4a99feb317bc2033874b41c3fd7f126
Reviewed-on: https://gerrit.instructure.com/138758
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins
Product-Review: James Williams  <jamesw@instructure.com>
QA-Review: James Williams  <jamesw@instructure.com>

app/controllers/users_controller.rb

@@ -2385,7 +2385,7 @@ class UsersController < ApplicationController
     end
 
     @user ||= @pseudonym && @pseudonym.user
-    @user ||= User.new
+    @user ||= @context.shard.activate { User.new }
 
     force_validations = value_to_boolean(params[:force_validations])
     manage_user_logins = @context.grants_right?(@current_user, session, :manage_user_logins)

spec/apis/v1/users_api_spec.rb

@@ -834,6 +834,20 @@ describe "Users API", type: :request do
         create_user_skip_cc_confirm(@site_admin)
       end
 
+      context "sharding" do
+        specs_require_sharding
+        it "should allow creating users on cross-shard accounts" do
+          @other_account = @shard1.activate { Account.create! }
+          json = api_call(:post, "/api/v1/accounts/#{@other_account.id}/users",
+            { :controller => 'users', :action => 'create', :format => 'json', :account_id => @other_account.id.to_s },
+            { :user => { :name => "Test User" }, :pseudonym => { :unique_id => "test@example.com", :password => "password123"} }
+          )
+          new_user = User.find(json['id'])
+          expect(new_user.shard).to eq @shard1
+          expect(new_user.pseudonym.account).to eq @other_account
+        end
+      end
+
       it "respects authentication_provider_id" do
         ap = Account.site_admin.authentication_providers.create!(auth_type: 'facebook')
         api_call(:post, "/api/v1/accounts/#{Account.site_admin.id}/users",