custom user store

Hi,

instead of using the UME user store i want to develop my own one.

Now i'm trying to implement the both interfaces

GroupContextSpi and UserContextSpi from the com.sap.engine.interfaces.security.userstore.spi package.

But i can not find any documentation and i'm not sure how to use these interfaces correctly.

Can anyone help me with a link or a tutorial?

Or is my way completely wrong?