FreeRADIUS authentication through Azure Active Directory

Question

I have just configured FreeRadius, but I would like to authenticate users which are in an Azure AD. I know it's possible to link FreeRADIUS with an Active Directory, but I can't find anything about Azure AD.
Does anyone knows if it's possible? A possible solution could be to create an AD locally synchronized with the Azure AD, but I would like to do it directly.

Answer 1

I did it with a little difficulty. John Robert Mendoza is correct but there are a few gotchas. Here are my steps:

1. Add AADDS and LDAP to AAD https://docs.microsoft.com/en-us/azure/active-directory-domain-services/active-directory-ds-admin-guide-configure-secure-ldap. (Secure ports as you are now open to a brute force attack.)
2. Create a linux vm (I used Ubuntu) to host Freeradius in the same vnet as your AADDS
3. Install freeradius 3.x with ldap
   sudo apt install freeradius
   sudo apt install freeradius-ldap
4. Configure freeradius (I will just outline the ldap to AAD configuration)
   i. edit /etc/freeradius/3.0/mods-available/ldap

These are the values I changed

    ldap {
        server = 'yourAADDSdomain.onmicrosoft.com'
        #the identity user should be a member of you AADDS admin group
        identity = '[email protected]' 
        password = 'yourpassword'
        basedn = 'OU=AADDC Users,dc=yourAADDSdomain,dc=onmicrosoft,dc=com'
        user {
           filter = “(userPrincipalName=%{%{Stripped-User-Name}:-%{User-Name}})”
        }
    }

ii. edit /etc/freeradius/3.0/sites-available/default

server default {
    listen {
        type = auth
        ipaddr = *
        port = 0
        limit {
              max_connections = 16
              lifetime = 0
              idle_timeout = 30
        }
    }
    listen {
        ipaddr = *
        port = 0
        type = acct
        limit {
        }
    }
    authorize {
         if (!control:Auth-Type) {
              ldap
              if (ok && User-Password) {
                      update {
                      control:Auth-Type := LDAP
                      }
              }
        }
        expiration
        logintime
    }
    authenticate {
        Auth-Type LDAP {
               ldap
        }
    }
    preacct {
        preprocess
        acct_unique
    }
    accounting {
        detail
        unix
        radutmp
        exec
        attr_filter.accounting_response
    }
    session {
        radutmp
    }
    post-auth {
        exec
        Post-Auth-Type REJECT {
                attr_filter.access_reject
        }
    } 
    pre-proxy {
    }
    post-proxy {
        eap
    }
}

Some other points:
Use radtest to test this out
use ldp.exe from a windows machine to connect to your ldap to check out what it is returning

links:
https://docs.microsoft.com/en-us/azure/active-directory-domain-services/active-directory-ds-admin-guide-configure-secure-ldap
https://wiki.freeradius.org/guide/Getting-Started
https://medium.com/@georgijsr/freeradius-2-1-12-ubuntu-14-04-server-with-ldap-authentication-and-ldap-fail-over-6611624ff2c9
Freeradius + Openldap ERROR: No authenticate method (Auth-Type) found for the request: Rejecting the user
http://freeradius.1045715.n5.nabble.com/guide-on-configuring-freeradius-3-LDAP-td5748776.html