A company I work for develops winforms .net applications in which users are required to login. These applications are deployed in an online environment, e.g desktops in a LAN where the client app connects to a service on a server. The same applications can be deployed 'standalone' in an offline environment, where data is occasionally synced back to the head office whenever there is a connection available.
The head office has an LDAP (Active Directory), but the disconnected environments don't.
Currently, each application has it's own login/password table in a database.
What is a good approach to implement a unified login/password or other authentication mechanism for all custom developed winforms applications in both online and offline situations (?), without
Is there a way to do this with windows authentication?
EDIT: it doesn't absolutely have to work with AD, but it does have to work offline.
What you are looking for is a single-sign-on solution. Active Directory fits the bill just fine here, you will find it difficult to implement something else on your own. I am not an expert on this one, but as far as I know Active Directory works offline too because profile information is replicated on clients.
For each of your applications, you would then write an ActiveDirectory adapter to authenticate the current AD user against your application.
For the exact details (esp. offline scenario but I'm 100% sure they are supported) you should consult an AD expert. Consider moving this question to Serverfault.