Looking for LDAP support

Ok, I am trying to use Active Directory authentication only to grant access to specific shares. I do not want the device tied to Active Directory, I simply need to read AD to verify that a user is a member of a specific group, or groups. I have a read only accout to preform the look up and group check, but the device seems to require that it be joined to the domain, and then managed by the AD administrator. This device will be used by a security group, which does not want others to have access to the device. If NetGear does not offer a software upgrade to allow LDAP read to check and grant access to the shares, is there an open source alternative or add on to allow authentication only via LDAP on the device?

Thank you for your response in advance.