Web FrameWork for User and Group Management

We are developing a Web app and looking for a solid existing framework/app that has User 开发者_运维技巧Management, Group Management, login screens, Group Admin screens, User SignUp, etc ... I have a feeling that all SaaS providers require such a thing and there should be something existing and I dont need to write everything again. I have searched google but could not find any such thing but I am sure there is something like this as it is such a basic requirement for any Web App. It can either be in the form of a separate server or can integrate into our app, language is not important for us. Easy integration and customization is most important

Our Cloudseal platform handles user and group management, login, reset password, lock account etc. It's currently used primarily for intranet and extranet applications i.e. there is no end user sign up screen but we do have a REST interface so you could collect user details on your site and make a REST call to register them in Cloudseal.