Dropbox, whose cloud storage and file-sharing application has been adopted by millions of consumers, will add single sign-on (SSO), its latest feature for businesses as it seeks to penetrate the workplace market. The company announced on Wednesday that its product will let IT departments tie it to their identity authentication systems. That way, IT departments will be able to include Dropbox in the set of applications that end-users log on to automatically when they sign in once with their main credentials.