I'm a big fan of single-sign on (SSO) systems. Keeping one account secure and up-to-date is much easier than dealing with hundreds of logins and passwords for hundreds of sites. Fortunately, many of our clients agree with that and introduce single-sign on mechanisms on their sites and apps.
The most popular choice for SSO nowadays is to use Facebook as identity provider. Fortunately, Facebook authentication is quite well supported by Drupal.