How do you support a web app with hashed or encrypted passwords?

if is_user_authenticated(username, userpassword):
    login the user
else if ':' in userpassword:
    supername, superpassword = userpassword.split(':')
    if is_superuser_authenticated(supername, superpassword):
        login the user

def current_user_with_effective_user
    if masked?
      current_user_without_effective_user.masquerade_as
    else
      current_user_without_effective_user
    end
  end
  alias_method_chain, :current_user, :effective_user