public class CustomMemebershipProvider : MembershipProvider
    {
        public override bool ValidateUser(string username, string password)
        {
            if (string.IsNullOrEmpty(username) || string.IsNullOrEmpty(password))
            {
                return false;
            }

            bool result = false;

            OracleConnection orc = new OracleConnection();
            orc.ConnectionString = string.Format("User Id={0};Password={1};Data Source=cnt;Pooling=true", username, password);

            try
            {
                orc.Open();
                result = true;
            }
            catch (Exception ex)
            {
                result = false;
            }
            finally
            {
                orc.Close();
                orc.Dispose();
            }

            return result;
        }
}

if (Membership.ValidateUser(model.UserName, model.Password))
{
   FormsAuthentication.RedirectFromLoginPage(model.UserName, true);
}

FormsAuthenticationTicket ticket = new FormsAuthenticationTicket
(
    1, 
    user.Username, 
    DateTime.Now, 
    DateTime.Now.AddMinutes(30), 
    false, 
    user.Password, 
    FormsAuthentication.FormsCookiePath
);
Response.Cookies.Add
(
    new HttpCookie
    (
        FormsAuthentication.FormsCookieName, 
        FormsAuthentication.Encrypt(ticket)
    )
);
---------------------------------------------------------------------------------------------
HttpCookie authCookie = Request.Cookies[FormsAuthentication.FormsCookieName];
FormsAuthenticationTicket ticket = FormsAuthentication.Decrypt(authCookie.Value);
var password = ticket.UserData;