As our most active customers needed to remember five different username-password combinations to use our services, it became painfully clear we needed a single sign on system. We looked at a few different systems, but Auth0 allowed us to use a single system for all our B2C, B2B and B2E requirements, had very reasonable pricing and provided a great deal of flexibility thanks to its use of Rules, Hooks, Extensions and Hosted Pages.
You can use any combination of identity providers, without having to make any changes to your app. You can even enable a different set of providers for different applications. We use passwordless, social and database login and plan to add Active Directory soon too.
Integrating Auth0 is incredibly easy, fast and flexible. With just a few lines of code, you're up and running, no matter if you need OAuth2, OpenID Connect or SAML. It provides great quick starts, clear documentation and quick support, both through the community forum and support desk. We're currently running it with various Node.js, PHP and Ruby applications.
All in all, Auth0 provides us with a common user identity across our applications and allows us to focus on the features of our applications, instead of having to spend hours and hours on creating safe login systems.