We are upgrading custom membership provider which is built on the top of dotnetnuke membership provider (version 6.1.5). My mistake, it is DotNetNuke.Provider.AspNetProvider assembly which we used. We created a class "MyMembershipProvider" and inherited from "AspNetMembershipProvider" class and implemented its methods and it works. following is the code example,

namespace DotNetNuke.Security.Membership
{
     public class MyMembershipProvider : AspNetMembershipProvider
     {
          public override UserInfo GetUserByUserName(int portalId, string username)

          {

          }

        public override UserInfo UserLogin(int portalId, string username, string password, string authType, string verificationCode, ref UserLoginStatus loginStatus)             {

         }

        //Implemented some other methods

However, I am trying to create same custom membership provider in clean dnn 8.0.4 version but I don't see this assembly in this version. Please suggest us how to go ahead? Please let me know if you need more information.