[8.17](backport #5988) Add support for pre existing Active Directory user

[mergify]

Waiting on custom windows image for testing with AD e2e.

New flags are introduced

• user
• group
• password (windows only)

These flags are taken into account only when --unprivileged is used.

New user is added same permissions as elastic-agent user when created in order to be able to log on as a service (otherwise agent won't start)

Custom user won't be created and needs to be present

Testing steps

Create a windows VM (windows server 2022)

Run script 1 that will prepare Active Directory

Script will also wait for AD services to start

$domainname = 'testing.local'
$addsSecurePass = ConvertTo-SecureString 'Changeme123+' -AsPlainText -Force

# install ad domain services
Install-WindowsFeature -name AD-Domain-Services -IncludeManagementTools


# setup pass for administrator to conform to forest requirements
net user Administrator 'Changeme123+' /passwordreq:yes

# add a new forest testing.com
Install-ADDSForest -DomainName $domainname -InstallDNS -ErrorAction Stop -NoRebootOnCompletion -SafeModeAdministratorPassword $addsSecurePass -Confirm:$false 

# reboot needs to be performed so changes are effective

Reboot to make changes effective

Run script that will prepare user

$domainname = 'testing.local'
$addsSecurePass = ConvertTo-SecureString 'Changeme123+' -AsPlainText -Force

# wait for AD to boot up
$domainFound = $true

$newObjectParameters = @{
    TypeName = 'System.DirectoryServices.ActiveDirectory.DirectoryContext'
    ArgumentList = @(
        "Domain"
        $domainname
    )
}

$DirectoryContext = New-Object @newObjectParameters

$startDate = Get-Date
do {
    try
    {
        [System.DirectoryServices.ActiveDirectory.DomainController]::FindOne($DirectoryContext)
        $domainFound = $true
    }
    catch
    {
        $domainFound = $false
        Start-Sleep -s 2
    }
} until ($domainFound -and $startDate.AddMinutes(5) -gt (Get-Date))


# add user
New-ADUser -Name 'TestingUser' -AccountPassword $addsSecurePass -Enabled $true -ChangePasswordAtLogon $false -PasswordNeverExpires $true

Scenario 1

• install as unpriviledged elastic-agent install --unprivileged --user="testing.local\TestUser" --password=Changeme123+
• check permissions are set to user and service is running as this user

Scenario 2

• install as admin
• switch to unpriviledged elastic-agent unprivileged --user="testing.local\TestUser" --password=Changeme123+
• check permissions are set to user and service is running as this user

Resolves #4585

---

This is an automatic backport of pull request #5988 done by Mergify.

[elastic-sonarqube]

Quality Gate failed

Failed conditions
0.0% Coverage on New Code (required ≥ 40%)

See analysis details on SonarQube