ActiveDirectoryLookup.rb

class ActiveDirectoryLookup  
def self.find_users(filter)
    base = "DC=lp,DC=local"
    users = []
    ldap_base.search(base: base, filter: filter) do |entry|
      users << { name: entry[:name].first, login: entry[:sAMAccountName].first, mail: entry[:mail].first, title: entry[:title].first}
    end
    return users
  end

  def self.ad_users_by_role(role)
    if role.filter then
      return ActiveDirectoryLookup.find_users(role.filter)
    else
      filter = "(memberOf=#{role.dn})"
      return ActiveDirectoryLookup.find_users(filter)
    end
  end
end

user.rb

class User
  [...]
  def has_role?(role)
    logins = self.logins.collect { |login| login.login.downcase}
    roles = ActiveDirectoryLookup.ad_users_by_role(role).collect{ |user| user[:login].downcase }
    (logins & roles).length > 0
  end
 end