How to integrate devise and rademade_admin

Given separate model for different authentication methods:

class Identity < ApplicationRecord

  belongs_to :user, autosave: true

  devise :database_authenticatable, :lockable, :registerable, :recoverable, :rememberable,
    :trackable, :validatable, :confirmable,  :encryptable, :omniauthable,
    omniauth_providers: [:facebook, :google_oauth2, :linkedin, :twitter, :vkontakte],
end

In order to give user access to admin panel you need to add three methods:

class User < ApplicationRecord
  has_many :identities, dependent: :destroy

  def self.get_by_email(email)
    find_by(email: email)
  end

  def valid_password?(password)
    email_identity.try(:valid_password?, password)
  end

  def email_identity
    identities.find_by(provider: 'email')
  end
end