module-and-template-store/app/models/api_key.rb

class ApiKey
  include Mongoid::Document
  field :access_token, type: String

  index({ access_token: 1}, { unique: true })

  before_create :generate_access_token
  
private
  
  def generate_access_token
    begin
      self.access_token = SecureRandom.hex
    end
  end
end