Create User from managed trigger

Hi all
I want to create user automatically when a record inserted to a specific table.
So I think that the best way is to write a managed trigger for "on inserted".
but in a managed trigger I can't add reference to System.Web.Security, so I can't use Membership.CreateUser method.
I spend so much time to find the way of encryption of password in application but I can't.
So can anyone help me.
Thanks in advance.

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