Since I'm flush with APC gear at the moment, I've been working with the network management devices (obviously, since I wrote Cacti and Nagios plugins for most of them). One of the features of most of the hardware is the ability to use local or RADIUS authentication. Obviously, with a large number of devices, using centralized authentication is not just a good idea, it's the only way to fly. Unfortunately, none of the NMCs have straight-up LDAP auth, but they will do RADIUS. Thus, using Microsoft's IAS (Internet Authentication Service) -- their interpretation of a RADIUS server, it's possible to do auth to AD via RADIUS though it's not exactly straightfoward.
APC has a knowledgebase document that describes a RADIUS implementation using FreeRADIUS. I'm a big FreeRADIUS fan, having used it in countless UNIX and dialup scenarios. However, it won't authenticate to AD without some serious gyrations, and it's simpler to use IAS. In order to use IAS, however, custom attributes need to be defined, otherwise logins may work but the admin bit will not be set and administration of the devices will be impossible. Here's the remedy.
Install IAS on a Windows server and register it with AD. Then, define a client. The client should be configured with any friendly name, and the IP of the NMC card in the APC device. Set the vendor to RADIUS Standard, and define the shared secret you'll be using. Next, define a new Remote Access Policy. Add some conditions, such as Windows-Groups matches "DOMAIN\Domain Admins" AND Client-IP-Address matches "172.16.1.*", which would cause this policy to only grant access if the user account is in the Domain Admins group, and the client IP falls within the 172.16.1 network. It's a good idea to restrict access in this way, since IAS RADIUS policies stop on the first match -- if you have multiple policies, you want them to be specific to their task.
Once this is done, some custom attributes have to be defined to grant admin privs to the user logging into the APC gear. Click Edit Profile with in the policy properties page. Click the Advanced tab, and Add an attribute. Select Vendor-Specific, and then click Add. Click Enter Vendor Code, and enter 318 into the text field to the right. Then, click Yes, it conforms, and then click Configure Attribute. Set the Vendor Assigned Attribute Number to 1, Attribute Format to "Decimal", and the Value to 1. This specifies that the value of attribute number 1, with Vendor Code 318 should be a decimal (integer) and be set to 1. The other possible values are 2, which denotes a device login, or 3, which is a read-only login, and is the default if this attribute is not defined. Note that by defining another policy that might match on a different set of groups, and setting this value to "3" will result in those users getting read-only access to the same devices, which might be handy.
Click OK a few times to get back to the Profile settings dialog, and select Authentication. make sure CHAP and PAP are selected, then click Apply and OK. Make sure that "Grant remote access permission" is selected, and click OK again. At this point, the server should be configured properly for the one RADIUS client originally specified. I usually stop and restart the IAS server at this point, since I've seen it act oddly when this isn't done.
Now, log into the APC device and configure RADIUS authentication. This is usually found on the Administration tab, under Security/Remote Users. Note that this has been tested with APC app module v3.3.1, and aos 3.3.4. If you haven't updated to this revision of the firmware on your devices, it's well worth the time to do so before continuing. Prior revisions may not even support RADIUS auth, for instance.
Fill in the server IP address and shared secret, then test the authentication. Assuming it works, set the authentication selection to "RADIUS, then Local Authentication", log out and then log back in with an account that matches the Remote Access policy defined on the IAS server. You should be in like Flynn.
I've run into some issues with using Network PowerChute with RADIUS authentication -- namely, the Network PowerChute service will not properly authenticate to a UPS NMC card that's configured for RADIUS auth, even with valid RADIUS credentials. I'm working with APC on a solution to that issue now, but I've tested this configuration with APC managed rack PDUs and air units without issue.