Attribute-Based Active Directory Group Membership

Unfortunately Active Directory doesn’t yet provide dynamic security groups in the way that, for example, Exchange provides dynamic distribution groups.  Sometimes it is useful to maintain a group’s membership based on a specific attribute, or set of attributes.  Here’s a quick Powershell example that shows how to maintain the membership based on the presence of a single attribute value.

You can download the script here: AttributeBasedGroupMembership

#########################################################
#
# Name: AttributeBasedGroupMembership.ps1
# Author: Tony Murray
# Version: 1.0
# Date: 18/06/2015
# Comment: PowerShell 2.0 script to manage group 
# membership based on attribute values
#
#########################################################

# Import the AD module
ipmo ActiveDirectory

# Define arrays to be used for matching
$arratt = @()
$arrgp = @()

# Domain controller to be used
$dc = (Get-ADRootDSE).dnshostname
write-host "Using DC $dc for all AD reads/writes"

# Specify the OU where the accounts are located
$OUdn = "OU=Corp Users,DC=Contoso,DC=com"

# Find all the objects that have the specified attribute value
$AttUsrs = Get-ADUser -LDAPFilter "(extensionattribute1=Sales)" -SearchBase $oudn -Server $dc

# Specify the GUID of the group to use
# You could also use name of group (but this can be changed)
$grp = "7bbf64bc-46c7-4a90-9d58-7cb5eca35fce" # i.e. "Sales Team"

# Find all the group members
$grpusers = Get-ADGroupMember -Identity $grp -Server $dc

# Build arrays using the DN attribute value
$AttUsrs | % {$arratt += $_.distinguishedname}
$grpusers | % {$arrgp += $_.distinguishedname}


# Add to group membership (newly assigned attribute value)
foreach ($usr in $arratt) {
    if ($arrgp -contains $usr) {
        write-host "User $usr is a member of the group"
    }
    else {
        write-host "User $usr is not a member of the group - adding..."
        Add-ADGroupMember -Identity $grp -Members $usr -Server $dc
    } # end else
    Remove-Variable -ErrorAction SilentlyContinue -Name usr    
} # end foreach

write-host "`n"

# Remove from group (no longer has attribute value or has been manually added to group)
# Assumption here is that the attribute value is authoritative for the group's membership
foreach ($mem in $arrgp) {
    if ($arratt -contains $mem) {
        write-host "User $mem still has the attribute value.  Nothing to do"
    } # end if
    else {
        write-host "User $mem does not have the attribute value.  Removing from membership..."
        Remove-ADGroupMember -Identity $grp -Members $mem -Server $dc -Confirm:$false
    } # end else
    Remove-Variable -ErrorAction SilentlyContinue -Name mem
} # end foreach

To ensure the script is run regularly, you would likely want to call it from a scheduled task.