The main problem is that I can't register or affect on the actual authentication in sitefinity by my own membership provider. Please, can you discribe step by step, what should I do, to get things work, like how should I implement my membership provider and attach it to sitefinity?
Also, do you have any documentation for developers, which will describe this type of solution in depth? I will appreciate if you give me some links to read.
CustomMembershipProvider : MembershipDataProvider
No, in this case I didn't. My MembershipProvider was getting it's data out of one of the Dynamic Modules within Sitefinity. But of course you can use a different connection string.