KB ID 0000688
I will say that Kerberos Authentication is a LOT easier to configure, so you might want to check that first.
Step 1 Configure the ASA for AAA RADIUS Authentication
2. In the Server group section > Add.
3. Give the group a name and accept the defaults > OK.
4. Now (with the group selected) > In the bottom (Server) section > Add.
Configure AAA RADIUS from command line;
aaa-server PNL-RADIUS protocol radius aaa-server PNL-RADIUS (inside) host 172.16.254.223 key 123456 radius-common-pw 123456 exit
Step 2 Configure Windows 2012 Server to allow RADIUS
7. On the Windows 2008 Server > Launch Server Manager > Roles > Add Role.
8. If you get a welcome page > Next > Select Network Policy and Access Server > Next >Next.
9. Select ‘Network Policy Server’ > Next > Install.
10. Close, when complete.
11. Whilst still in Server Manager > Network Policy and Access Server > NPS (Local).
12. Register Server in Active Directory >OK > OK.
14. Give the firewall a friendly name, (take note of what this is, you will need it again) > Specify its IP > Enter the shared secret you setup above (number 5) > OK.
15. Expand policies > right click ‘Connection Request Policies’ > New > Give the policy a name > Next.
16. Add a condition > Set the condition to ‘Client Friendly Name’ > Add.
17. Specify the name you set up above (number 14) > OK > Next > Next > Next.
18. Change the attribute to User-Name > Next > Finish.
19. Now right click ‘Network Policies’ > New > Give the policy a name> Next.
20. Add a condition > User Groups > Add.
21. Add in the AD security group you want to allow access to > OK > Next > Next.
Step 3 Test RADIUS Authentication
23. Back at the ASDM, in the same page you were in previously, select your server and then click ‘Test’.
24. Change the selection to Authentication > Enter your domain credentials > OK.
25. You are looking for a successful outcome.
Note: if it fails check there is physical connectivity between the two devices, the shared secrets match. Also ensure UDP ports 1645 and 1646 are not being blocked.
To Test AAA RADIUS Authentication from Command Line
test aaa-server authentication PNL-RADIUS host 172.16.254.223 username petelong password password123
26. Finally, save the firewall changes > File > Save running configuration to flash.