Essaye qq chose comme ça (avec seulement le gem ruby-net-ldap) :

require "net/ldap"
LDAP_HOST = "..."
LDAP_MASTER_DN = "CN=un compte de référence,DC=la_base"
LDAP_MASTER_PWD = "le pass"
LDAP_BASE = "dc=la_base"

def ldap_authenticate( logname, password )

return [:auth_fail, nil] if logname.empty? or password.empty?

begin
ldap = Net::LDAP.new
ldap.host = LDAP_HOST
ldap.port = 389
ldap.authenticate LDAP_MASTER_DN, LDAP_MASTER_PWD

result = ldap.bind_as :base => LDAP_BASE, :filter=> "(AccountName=#{logname})", :password=>password
return [:auth_ok, result] if result
return [:auth_fail, nil] if ldap.bind
rescue Net::LDAP::LdapError => e
end
return [:server_error, nil]

end

status, dn = ldap_authenticate( logname, password )

full_name = dn.first.displayname.to_s if status == :auth_ok

Voilà, je ne suis pas un pro de ldap mais ça semble fonctionner.

Bonne chance
Benoit