Adding a user to many security groups in Active Directory using PowerShell is simple. You can use the Add-ADPrincipalGroupMembership cmdlet. This cmdlet allows you to add a user to one or more security groups.

Here’s an example of how you might use this cmdlet (this is an OK solution):

# Define the user you want to add to the security groups
$user = Get-ADUser -Identity "Jeffrey"

# Define the security groups you want to add the user to
$groups = @("DelegatedDomainJoiner", "App1_RO", "App2_Admin")

# We now use a foreach loop to add the user to each group
foreach ($group in $groups)
{
    Add-ADPrincipalGroupMembership -Identity $user -MemberOf $group
}

The Add-ADPrincipalGroupMembership cmdlet, is used inside a foreach loop. The user stored in the $user variable to each security group stored in the $groups array. But this method requires you to loop through all the groups and add the user to each one. This is OK, but we can do it a bit better from code readability standpoint.

We can use the -Members parameter of the Add-ADGroupMember cmdlet instead. To add the user to many security groups at once, take a look at the example below (this is a BETTER solution):

# Define the user you want to add to the security groups
$user = Get-ADUser -Identity "Jeffrey"

# Define the security groups you want to add the user to
$groups = @("DelegatedDomainJoiner", "App1_RO", "App2_Admin")

# This command will add the user to all the groups at once
Add-ADGroupMember -Identity $groups -Members $user

Here, we are using the Add-ADGroupMember cmdlet. The user stored in the $user variable to all the security in a single command. I find this method to be much more concise.

Note: Of course, you will need the correct permissions in Active Directory and the Active Directory PowerShell module.