I we have created a website that requires users to login. It used forms based authentication and sql server to validation the login credentials.
Should we need to purchase an external connector license from microsoft to be able to host this site on a windows .net platform.
Edit: More information about external connectors. In microsoft licensing world there are cals for users connecting to the windows server software, external connectors are unlimited cal licenses.
What external connector? As long as you have licences for Windows (the Server versions are recommended) and SQL Server you could host your site without needing to purchase additional licenses. Install .NET and IIS on the web server and there shouldn't be any problems. If by connector you mean database driver then it is already built into the framework (ADO.NET).
Not needed. They are needed to use - if you are a company - AD (Active DIrectory) for the external users. As you do all the authentication within your application, the app does not need a CAL. Obviously users are limited (no windows services file access etc.), but this is what you actually want.
Note through that depending on your business type you may HAVE to license OS / Database via SPLA - and the normal license may simply not cover you at all. Good news: this means cheap access to Web editions and only monthly payment - pretty low. Depends really on your business model and what the application does.