OAuth is an open protocol that enables users to share their protected resources among different Web sites, without risking exposure. OAuth is an ideal candidate for mashing up today's social networking Web sites like Twitter. The first part of this series gives an introduction to OAuth, followed by an example of the development of an OAuth-enabled desktop Twitter client. The second part of this series demonstrates how to develop an OAuth-enabled Web Twitter client, which will be migrated to Google App Engine (GAE) in the third and final part of the series.