How to create a centralized user database

My company creates a lot of applications that have very similar functionality, with a few differences between each one. For example, some 开发者_运维技巧sites have a group creation feature, others have user profile pages, and yet others allow users to accumulate achievement points and such.

Our clients want users to be able to log in to each application with the same username/password, since it doesn't really make sense for the user to have to register a different account for each site.

How do we design our database? Is it better to have a single central database for all of our applications, or separate them into individual databases and do JOINs across databases? Which is better performance-wise and design-wise?

Thanks for any insight!

Just go with OpenID. Simplest to just use Facebook Connect as a provider. They let you get to all of your user's data (like name etc.) so you can identify and data mine them if need be.

If you don't want to rely on an external provider to handle your user accounts, then become your own OpenID provider.

I would have a central server, which hosts a user db and web services to access that user db.

That way you can use the same DB, and perform logins over web services to that system from your front end.

This is also scalable and can grow in complexity with your applications.

I would take the other two answers and combines them to make a private OpenId Provider.

This way you can use the standard OpenId clients for your developments, and possibly even open your applications up for external OpenId providers if you developments need them.

This gives scalability and open standards for other applications within the organisations to use the same provider.

In a general way I would develop tables that would be Master Data, they will be single version of the truth application wide. Each and every application will access the same "clients base". In your case it seems that the concept of Master Data can be applied to your applications database.

If the applications are hosted within the company you can use active directory. You can access active directory from php with the ldap functionality. You can than add users to groups in active directory to give them access to various functionality within the application.