feat(bootstrap): two-stage loader and Authenticode-signed customer scripts (D-224)

Start-AutopilotMonitor.ps1 is the new stage 1 -- the file an administrator assigns in Intune. It carries no enrollment logic: it downloads the published installer, verifies its Authenticode signature, and runs it in the same process, passing through every remaining argument. Assigning the installer directly stays supported and unchanged. The point of the split is that the customer-held artifact stops changing. Today every bootstrap change forces customers to replace their Intune copy, so the fleet runs a distribution of script versions we do not control. It is also what makes script signing worth doing: signing a file that gets swapped by hand each release is a one-off gain, signing a loader that never changes is permanent. The loader is deliberately minimal, because it is the one piece that cannot be fixed remotely -- every guard placed in it would be frozen for years. All guards stay in stage 2. Verification pins the certificate SUBJECT, never a thumbprint: certificates get renewed and a deployed loader cannot be, so a thumbprint pin would strand the fleet at the next renewal. A hash oracle was rejected for a different reason -- it would have to be fetched from the same host as the script, so it could not survive a compromise of that host, while the expected publisher travels inside the loader. Fail-closed on verification, fail-soft on exit: nothing runs without a valid signature from us (running unverified code as SYSTEM is the risk being removed here), but the loader still exits 0, because a device without monitoring is acceptable and a failed enrollment step is not. The accepted cost is that a device which can never fetch or verify stays silent. Publisher changes: - every published script is signed (loader, installer, both -Dev renders, Test-ShouldBootstrapAgent, Grant-AutopilotMonitorAddOn), and signing is the LAST transformation: it covers exactly the CRLF/UTF-8 bytes Get-PublishBytes produced, so nothing may normalise or re-encode them afterwards. - signing is mandatory for a real publish. Only -DryRun may run unsigned, because the PR gate executes the publisher without any Azure login. - comparisons against a published copy strip the signature block first. A timestamped signature differs on every run, so without stripping the version-bump guard and the drift check would report a change for every unchanged script. - the bump guard became Assert-VersionBump and now covers the loader as well. - version.json gains loaderVersion. Additive, no consumer yet: stage 2 is current by construction, so only stage 1's version says anything about a customer's Intune copy. - -SignedOutputDir writes the exact uploaded bytes for the CI artifact, in a dry run too -- that is how a signed script gets inspected before it reaches anyone. publish-scripts.yml logs in with the signing identity first and only to fetch the Key Vault token (azure/login sets the default az account and the storage login has to be the one that stays), then publishes and offers the signed scripts as an artifact. build-agent.yml passes the same parameters on a stable cutover. Tests: 14 new Pester cases, including that a validly signed script from a FOREIGN publisher is refused -- that is what an attacker with any code-signing certificate can produce. Full bootstrap suite on Windows PowerShell 5.1: 43/43. Not covered: the MSI runner still downloads stage 2 without verifying it, and the customer docs still describe the direct assignment only. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
2026-10-24 04:32:32 +00:00 · 2026-09-08 18:48:21 +02:00
parent 9c1d0586ef
commit 0ac548bfce
6 changed files with 634 additions and 49 deletions
@@ -16,20 +16,30 @@
    enrolling device, so "current" is a correctness property, not cosmetics.

    Steps, in order:
-      1. Parse $ScriptVersion from the bootstrap source.
-      2. Render the -Dev variant by literal substitution of the two URL/manifest
+      1. Parse $ScriptVersion from the loader and the bootstrap source.
+      2. Render the -Dev variants by literal substitution of the URL/manifest
         defaults. A missing anchor is a hard failure -- a silently un-substituted
         dev script would point the dev fleet at the stable agent.
-      3. Version-bump guard: if the published bootstrap differs from the source
-         but carries the same $ScriptVersion, abort. Otherwise the docs badge,
+      3. Version-bump guard: if a published script differs from its source but
+         carries the same $ScriptVersion, abort. Otherwise the docs badge,
         version.json.bootstrapVersion and the portal's "your script is outdated"
         hint would all keep asserting a version that is no longer what ships.
-      4. Upload every script blob with Cache-Control: no-cache (they rotate in
+      4. Build the publish set (loader, bootstrap, both dev renders, the extras).
+      5. Authenticode-sign every script (see -SigningToken). Signing is the LAST
+         transformation: it covers the exact CRLF/UTF-8 bytes that get uploaded,
+         and nothing may touch them afterwards or the signature breaks.
+      6. Upload every script blob with Cache-Control: no-cache (they rotate in
         place), mirrored fail-soft to the legacy account.
-      5. Reconcile the two version oracles: version.json.bootstrapVersion
-         (read-modify-write under If-Match, so a concurrent agent release cannot
-         lose its agent fields) and AdminConfiguration.LatestBootstrapV2ScriptVersion.
-      6. Verify through the alias -- re-download each blob and compare SHA-256.
+      7. Reconcile the version oracles: version.json.bootstrapVersion and
+         .loaderVersion (read-modify-write under If-Match, so a concurrent agent
+         release cannot lose its agent fields) and
+         AdminConfiguration.LatestBootstrapV2ScriptVersion.
+      8. Verify through the alias -- re-download each blob and compare SHA-256.
+
+    Comparisons against a published script always strip its signature block first
+    (Get-ComparableText). A signature carries a timestamp, so signed bytes differ on
+    every run; without stripping, the bump guard and the drift check would report a
+    change for every unchanged script.

 .PARAMETER LegacySasToken
    Container SAS for the legacy account. Optional -- a mirror failure warns, never fails.
@@ -40,18 +50,39 @@
    Repository root. Defaults to the parent of .github/scripts.

 .PARAMETER DryRun
-    Run every check and render, upload nothing.
+    Run every check and render, upload nothing. A dry run signs when a token is supplied
+    and skips signing when it is not: the PR gate runs this without any Azure login.
+
+.PARAMETER SigningToken
+    Azure Key Vault access token for AzureSignTool. MANDATORY for a real publish -- an
+    unsigned customer script is not something this repo publishes. Together with
+    -KeyVaultUrl and -CertificateName.
+
+.PARAMETER ExpectedPublisher
+    Optional -like pattern the signer subject must match after signing. Pins the publisher
+    instead of accepting any trusted signature; the loader on the device pins the same way.
+
+.PARAMETER SignedOutputDir
+    Optional directory that receives a copy of every published file exactly as uploaded.
+    Used by CI to offer the signed scripts as a build artifact for local inspection.

 .EXAMPLE
    ./Publish-BootstrapScripts.ps1 -DryRun

 .EXAMPLE
-    ./Publish-BootstrapScripts.ps1 -LegacySasToken $env:LEGACY_SAS
+    ./Publish-BootstrapScripts.ps1 -LegacySasToken $env:LEGACY_SAS -SigningToken $env:AKV_TOKEN `
+        -KeyVaultUrl $env:KV_URL -CertificateName $env:CERT
 #>
 [CmdletBinding()]
 param(
    [string]$LegacySasToken,
    [string]$RepoRoot,
+    [string]$SigningToken,
+    [string]$KeyVaultUrl,
+    [string]$CertificateName,
+    [string]$TimestampUrl = 'http://timestamp.acs.microsoft.com',
+    [string]$ExpectedPublisher,
+    [string]$SignedOutputDir,
    [switch]$DryRun
 )

@@ -69,8 +100,23 @@ $TableUrl           = "https://autopilotmonitoreu.table.core.windows.net/AdminCo
 $BootstrapSource   = Join-Path $RepoRoot 'scripts/Bootstrap/Install-AutopilotMonitor.ps1'
 $BootstrapBlob     = 'Install-AutopilotMonitor.ps1'
 $DevBlob           = 'Install-AutopilotMonitor-Dev.ps1'
+# Stage 1. What a customer assigns in Intune once; it downloads the bootstrap above on
+# every device and verifies its publisher before running it.
+$LoaderSource      = Join-Path $RepoRoot 'scripts/Bootstrap/Start-AutopilotMonitor.ps1'
+$LoaderBlob        = 'Start-AutopilotMonitor.ps1'
+$LoaderDevBlob     = 'Start-AutopilotMonitor-Dev.ps1'
 $ScriptContentType = 'text/plain; charset=utf-8'

+$SigningEnabled = -not [string]::IsNullOrWhiteSpace($SigningToken)
+if (-not $DryRun -and -not $SigningEnabled) {
+    throw ('Publishing requires -SigningToken (plus -KeyVaultUrl and -CertificateName): the ' +
+           'loader on every device verifies the publisher of what it downloads, so an unsigned ' +
+           'script would be rejected in the field. Only -DryRun may run without signing.')
+}
+if ($SigningEnabled -and ([string]::IsNullOrWhiteSpace($KeyVaultUrl) -or [string]::IsNullOrWhiteSpace($CertificateName))) {
+    throw '-SigningToken needs -KeyVaultUrl and -CertificateName.'
+}
+
 function Get-HttpStatus {
    param($ErrorRecord)
    if ($ErrorRecord.Exception.PSObject.Properties['Response'] -and $ErrorRecord.Exception.Response) {
@@ -116,6 +162,122 @@ function Get-PublishBytes {
    return ,(New-Object System.Text.UTF8Encoding $false).GetBytes($normalised)
 }

+# A PowerShell signature is appended as a comment block at the end of the file, so the
+# published bytes are "source + signature". Everything that compares a published script to
+# its source has to cut that block off first -- the signature carries a timestamp and is
+# therefore different on every publish, while the script above it is unchanged.
+function Remove-SignatureBlock {
+    param([string]$Text)
+    $marker = '# SIG # Begin signature block'
+    $index = $Text.IndexOf($marker)
+    if ($index -lt 0) { return $Text }
+    return $Text.Substring(0, $index)
+}
+
+# Comparison form: no signature, LF, no trailing blank lines. Used for "is the published
+# copy still this source" -- never for what gets uploaded.
+function Get-ComparableText {
+    param([string]$Text)
+    return (Remove-SignatureBlock $Text).Replace("`r`n", "`n").TrimEnd("`n")
+}
+
+# Signs the publish set in place: each item's bytes are written to a work directory, signed
+# there, verified, and read back as the bytes that will be uploaded. Signing has to be the
+# last transformation -- the signature covers exactly these bytes, so nothing may normalise
+# or re-encode them afterwards.
+function Set-PublishSetSignature {
+    param([object[]]$Items, [string]$WorkDir)
+
+    if (-not (Get-Command azuresigntool -ErrorAction SilentlyContinue)) {
+        throw "azuresigntool is not on PATH. Install it with: dotnet tool install --global AzureSignTool --version 7.0.1"
+    }
+
+    New-Item -ItemType Directory -Force -Path $WorkDir | Out-Null
+
+    $paths = @()
+    foreach ($item in $Items) {
+        $path = Join-Path $WorkDir $item.BlobName
+        [System.IO.File]::WriteAllBytes($path, [byte[]]$item.Bytes)
+        $paths += $path
+    }
+
+    Write-Host "Signing $($paths.Count) script(s) with certificate '$CertificateName'..."
+    & azuresigntool.exe sign --verbose `
+        --azure-key-vault-url $KeyVaultUrl `
+        --azure-key-vault-accesstoken $SigningToken `
+        --azure-key-vault-certificate $CertificateName `
+        --timestamp-rfc3161 $TimestampUrl `
+        --file-digest sha256 `
+        --description 'Autopilot Monitor bootstrap' `
+        --description-url 'https://www.autopilotmonitor.com' `
+        $paths
+
+    # Native tool: PowerShell does not throw on a non-zero exit, and an unnoticed signing
+    # failure would publish unsigned scripts that every loader in the field then rejects.
+    if ($LASTEXITCODE -ne 0) {
+        throw "azuresigntool failed with exit code $LASTEXITCODE -- nothing was uploaded."
+    }
+
+    foreach ($item in $Items) {
+        $path = Join-Path $WorkDir $item.BlobName
+        $sig = Get-AuthenticodeSignature -FilePath $path
+        if ($sig.Status -ne 'Valid') {
+            throw "Signature on $($item.BlobName) is '$($sig.Status)', expected 'Valid'."
+        }
+        # Without a timestamp the signature dies with the certificate, and these scripts sit
+        # on customer devices far longer than a certificate lifetime.
+        if (-not $sig.TimeStamperCertificate) {
+            throw "Signature on $($item.BlobName) carries no timestamp."
+        }
+        if ($ExpectedPublisher -and $sig.SignerCertificate.Subject -notlike $ExpectedPublisher) {
+            throw "$($item.BlobName) was signed by '$($sig.SignerCertificate.Subject)', expected '$ExpectedPublisher'."
+        }
+        $item.Bytes = ,([System.IO.File]::ReadAllBytes($path))
+        Write-Host "  signed $($item.BlobName) ($($item.Bytes.Length) bytes, signer $($sig.SignerCertificate.Subject.Split(',')[0]))"
+    }
+}
+
+# Aborts when a published script changed behaviour without a version bump. Consumers act on
+# the version (docs badge, version.json, the portal's outdated-script hint), so an unchanged
+# version has to mean unchanged behaviour.
+function Assert-VersionBump {
+    param(
+        [string]$BlobName,
+        [string]$SourceContent,
+        [string]$SourceOrigin,
+        [string]$SourceVersion
+    )
+
+    $publishedBytes = Get-PublishedBytes "$AliasUrl/$BlobName"
+    if ($null -eq $publishedBytes) {
+        Write-Host "No published $BlobName yet -- version-bump guard skipped (first publish)"
+        return
+    }
+
+    $publishedText = [System.Text.Encoding]::UTF8.GetString($publishedBytes)
+    if ((Get-ComparableText $publishedText) -eq (Get-ComparableText $SourceContent)) {
+        Write-Host "Published $BlobName is already this source (signature block aside)"
+        return
+    }
+
+    $publishedVersion = Get-BootstrapScriptVersion -Content $publishedText -Origin "$AliasUrl/$BlobName" -Optional
+
+    if ($null -eq $publishedVersion) {
+        Write-Host "::warning::The published $BlobName is not a readable script (no ScriptVersion found). Republishing over it."
+    } elseif ($publishedVersion -ne $SourceVersion) {
+        Write-Host "Version bump: $publishedVersion -> $SourceVersion ($BlobName)"
+    } elseif ((Get-CodeFingerprint -Text (Remove-SignatureBlock $publishedText) -Origin "$AliasUrl/$BlobName") -eq
+              (Get-CodeFingerprint -Text $SourceContent -Origin $SourceOrigin)) {
+        # Comments, typos in comments, reflow -- nothing a consumer of the version can act on.
+        Write-Host "::warning::$BlobName changed in comments or formatting only; publishing under the unchanged version $SourceVersion."
+    } else {
+        throw ("Version-bump guard: $BlobName changed behaviour but ScriptVersion is still $SourceVersion. " +
+               "Bump it in $SourceOrigin -- the docs badge, version.json and the " +
+               'portal outdated-script hint all read that value, and customers decide from it whether ' +
+               'to re-upload their Intune copy. Comment-only and formatting changes do not need a bump.')
+    }
+}
+
 function Get-BootstrapScriptVersion {
    param([string]$Content, [string]$Origin, [switch]$Optional)
    if ($Content -match '\$ScriptVersion\s*=\s*"([\d\.\-a-zA-Z]+)"') { return $Matches[1] }
@@ -143,12 +305,16 @@ function Get-CodeFingerprint {
    return (($tokens | Where-Object { $ignored -notcontains $_.Kind.ToString() } | ForEach-Object { $_.Text }) -join "`n")
 }

-# ------------------------------------------------------------------ 1. source
+# ------------------------------------------------------------------ 1. sources
 $sourceContent = Get-Content $BootstrapSource -Raw
 $sourceBytes   = Get-PublishBytes $sourceContent
 $scriptVersion = Get-BootstrapScriptVersion -Content $sourceContent -Origin $BootstrapSource
 Write-Host "Bootstrap script version: $scriptVersion"

+$loaderContent = Get-Content $LoaderSource -Raw
+$loaderVersion = Get-BootstrapScriptVersion -Content $loaderContent -Origin $LoaderSource
+Write-Host "Loader script version: $loaderVersion"
+
 # ------------------------------------------------------------------ 2. dev render
 $stableUrlLiteral = '$AgentDownloadUrl = "https://download.autopilotmonitor.com/agent/AutopilotMonitor-Agent.zip"'
 $devUrlLiteral    = '$AgentDownloadUrl = "https://download.autopilotmonitor.com/agent/AutopilotMonitor-Agent-dev.zip"'
@@ -161,33 +327,21 @@ if ($sourceContent.IndexOf($stableUrlLiteral) -lt 0 -or $sourceContent.IndexOf($
 $devContent = $sourceContent.Replace($stableUrlLiteral, $devUrlLiteral).Replace($stableManLiteral, $devManLiteral)
 Write-Host "Rendered $DevBlob (dev agent URL + version-dev.json)"

-# ------------------------------------------------------------------ 3. bump guard
-$publishedBytes = Get-PublishedBytes "$AliasUrl/$BootstrapBlob"
-if ($null -eq $publishedBytes) {
-    Write-Host 'No published bootstrap yet -- version-bump guard skipped (first publish)'
-} elseif ((Get-Sha256 $publishedBytes) -eq (Get-Sha256 $sourceBytes)) {
-    Write-Host 'Published bootstrap is already byte-identical to the source'
-} else {
-    $publishedText    = [System.Text.Encoding]::UTF8.GetString($publishedBytes)
-    $publishedVersion = Get-BootstrapScriptVersion -Content $publishedText -Origin "$AliasUrl/$BootstrapBlob" -Optional
+# The dev loader must fetch the dev bootstrap, or a dev device would run the stable chain.
+$stableLoaderLiteral = '$BootstrapUrl = "https://download.autopilotmonitor.com/agent/Install-AutopilotMonitor.ps1"'
+$devLoaderLiteral    = '$BootstrapUrl = "https://download.autopilotmonitor.com/agent/Install-AutopilotMonitor-Dev.ps1"'

-    if ($null -eq $publishedVersion) {
-        Write-Host "::warning::The published $BootstrapBlob is not a readable bootstrap script (no ScriptVersion found). Republishing over it."
-    } elseif ($publishedVersion -ne $scriptVersion) {
-        Write-Host "Version bump: $publishedVersion -> $scriptVersion"
-    } elseif ((Get-CodeFingerprint -Text $publishedText -Origin "$AliasUrl/$BootstrapBlob") -eq
-              (Get-CodeFingerprint -Text $sourceContent -Origin $BootstrapSource)) {
-        # Comments, typos in comments, reflow -- nothing a consumer of the version can act on.
-        Write-Host "::warning::$BootstrapBlob changed in comments or formatting only; publishing under the unchanged version $scriptVersion."
-    } else {
-        throw ("Version-bump guard: $BootstrapBlob changed behaviour but ScriptVersion is still $scriptVersion. " +
-               "Bump it in $BootstrapSource -- the docs badge, version.json.bootstrapVersion and the " +
-               'portal outdated-script hint all read that value, and customers decide from it whether ' +
-               'to re-upload their Intune copy. Comment-only and formatting changes do not need a bump.')
-    }
+if ($loaderContent.IndexOf($stableLoaderLiteral) -lt 0) {
+    throw "Loader dev-render: anchor literal missing in $LoaderSource"
 }
+$devLoaderContent = $loaderContent.Replace($stableLoaderLiteral, $devLoaderLiteral)
+Write-Host "Rendered $LoaderDevBlob (points at $DevBlob)"

-# ------------------------------------------------------------------ 4. upload
+# ------------------------------------------------------------------ 3. bump guards
+Assert-VersionBump -BlobName $BootstrapBlob -SourceContent $sourceContent -SourceOrigin $BootstrapSource -SourceVersion $scriptVersion
+Assert-VersionBump -BlobName $LoaderBlob    -SourceContent $loaderContent -SourceOrigin $LoaderSource    -SourceVersion $loaderVersion
+
+# ------------------------------------------------------------------ 4. publish set
 # Sources beyond the bootstrap pair, read straight from the repo.
 $extraSources = @(
    @{ Path = 'scripts/Bootstrap/Test-ShouldBootstrapAgent.ps1';       BlobName = 'Test-ShouldBootstrapAgent.ps1' }
@@ -197,15 +351,29 @@ $extraSources = @(
 # Uninstall-AutopilotMonitor.ps1 is deliberately NOT published: nothing links it, and
 # an unauthenticated uninstall script on the public download host is not a feature.

+# Text is the unsigned publish form and stays the reference for every comparison against a
+# published copy; Bytes is what goes on the wire and carries the signature after step 4.
 $publishSet = [System.Collections.Generic.List[object]]::new()
-$publishSet.Add([pscustomobject]@{ BlobName = $BootstrapBlob; Bytes = $sourceBytes })
-$publishSet.Add([pscustomobject]@{ BlobName = $DevBlob;       Bytes = (Get-PublishBytes $devContent) })
+$publishSet.Add([pscustomobject]@{ BlobName = $LoaderBlob;    Text = $loaderContent;    Bytes = (Get-PublishBytes $loaderContent) })
+$publishSet.Add([pscustomobject]@{ BlobName = $LoaderDevBlob; Text = $devLoaderContent; Bytes = (Get-PublishBytes $devLoaderContent) })
+$publishSet.Add([pscustomobject]@{ BlobName = $BootstrapBlob; Text = $sourceContent;    Bytes = $sourceBytes })
+$publishSet.Add([pscustomobject]@{ BlobName = $DevBlob;       Text = $devContent;       Bytes = (Get-PublishBytes $devContent) })
 foreach ($extra in $extraSources) {
    $extraPath = Join-Path $RepoRoot $extra.Path
    if (-not (Test-Path $extraPath)) {
        throw "Publish source missing: $extraPath"
    }
-    $publishSet.Add([pscustomobject]@{ BlobName = $extra.BlobName; Bytes = (Get-PublishBytes (Get-Content $extraPath -Raw)) })
+    $extraText = Get-Content $extraPath -Raw
+    $publishSet.Add([pscustomobject]@{ BlobName = $extra.BlobName; Text = $extraText; Bytes = (Get-PublishBytes $extraText) })
+}
+
+# ------------------------------------------------------------------ 5. sign
+# After this point the bytes are final. Normalising, re-encoding or rewriting a line ending
+# would invalidate the signature, and the device-side loader would refuse the script.
+if ($SigningEnabled) {
+    Set-PublishSetSignature -Items $publishSet -WorkDir (Join-Path ([System.IO.Path]::GetTempPath()) "apm-publish-$PID")
+} else {
+    Write-Host '::warning::No signing token supplied -- dry run continues with unsigned scripts.'
 }

 $legacySas = if ($LegacySasToken) { $LegacySasToken.TrimStart('?') } else { '' }
@@ -214,6 +382,7 @@ $legacySas = if ($LegacySasToken) { $LegacySasToken.TrimStart('?') } else { '' }
 # (bootstrap-script-gates.yml) executes this script with -DryRun and never logs in.
 $authHeaders = if ($DryRun) { $null } else { & (Join-Path $PSScriptRoot 'Get-StorageAuthHeaders.ps1') }

+# ------------------------------------------------------------------ 6. upload
 foreach ($item in $publishSet) {
    # Explicit type, not a convenience: an Object[] body is uploaded as space-separated
    # decimals rather than raw bytes, and every hash check still passes because [byte[]]
@@ -221,11 +390,21 @@ foreach ($item in $publishSet) {
    [byte[]]$bytes = $item.Bytes
    $item | Add-Member -NotePropertyName Sha256 -NotePropertyValue (Get-Sha256 $bytes) -Force

+    # Exactly the bytes that go on the wire, for the CI artifact. Written in a dry run too:
+    # that is the run an operator uses to inspect a signed script before it is published.
+    if ($SignedOutputDir) {
+        New-Item -ItemType Directory -Force -Path $SignedOutputDir | Out-Null
+        [System.IO.File]::WriteAllBytes((Join-Path $SignedOutputDir $item.BlobName), $bytes)
+    }
+
    if ($DryRun) {
-        # Doubles as a drift check: says per blob whether the alias already serves this source.
+        # Doubles as a drift check: says per blob whether the alias already serves this
+        # source. Compared as text without the signature block -- signed bytes differ on
+        # every run, so a byte comparison would report drift for every unchanged script.
        $served = Get-PublishedBytes "$AliasUrl/$($item.BlobName)"
        $state = if ($null -eq $served) { 'MISSING on the alias' }
-                 elseif ((Get-Sha256 $served) -eq $item.Sha256) { 'already current' }
+                 elseif ((Get-ComparableText ([System.Text.Encoding]::UTF8.GetString($served))) -eq
+                         (Get-ComparableText $item.Text)) { 'already current' }
                 else { 'STALE on the alias' }
        Write-Host "  [dry-run] $($item.BlobName) ($($bytes.Length) bytes, sha256 $($item.Sha256)) -- $state"
        continue
@@ -260,7 +439,7 @@ foreach ($item in $publishSet) {
    }
 }

-# ------------------------------------------------------------------ 5. version oracles
+# ------------------------------------------------------------------ 7. version oracles
 # version.json is the agent manifest; only bootstrapVersion belongs to us. Read from the
 # blob (not the alias) for an authoritative ETag, write back under If-Match so a concurrent
 # agent release cannot lose its version/sha256 fields.
@@ -272,11 +451,15 @@ if (-not $DryRun) {
        } else { [string]$manifestResp.Content }
        $manifest = $manifestRaw | ConvertFrom-Json

-        if ($manifest.bootstrapVersion -eq $scriptVersion) {
-            Write-Host "version.json already reports bootstrapVersion $scriptVersion"
+        if ($manifest.bootstrapVersion -eq $scriptVersion -and $manifest.loaderVersion -eq $loaderVersion) {
+            Write-Host "version.json already reports bootstrapVersion $scriptVersion and loaderVersion $loaderVersion"
        } else {
            $etag = '"' + ([string]($manifestResp.Headers['ETag'] | Select-Object -First 1)).Trim('"') + '"'
            $manifest | Add-Member -NotePropertyName 'bootstrapVersion' -NotePropertyValue $scriptVersion -Force
+            # Additive: no consumer reads loaderVersion yet. It exists so support can tell
+            # which stage-1 file a device was assigned -- stage 2 is always current by
+            # construction, so its version says nothing about the customer's Intune copy.
+            $manifest | Add-Member -NotePropertyName 'loaderVersion' -NotePropertyValue $loaderVersion -Force
            $body = [System.Text.Encoding]::UTF8.GetBytes(($manifest | ConvertTo-Json -Compress))
            $manifestHeaders = @{
                'x-ms-blob-type'          = 'BlockBlob'
@@ -285,7 +468,7 @@ if (-not $DryRun) {
                'If-Match'                = $etag
            }
            Invoke-RestMethod -Uri "$ContainerUrl/version.json" -Method Put -Headers ($authHeaders + $manifestHeaders) -Body $body | Out-Null
-            Write-Host "version.json bootstrapVersion -> $scriptVersion (agent fields untouched)"
+            Write-Host "version.json bootstrapVersion -> $scriptVersion, loaderVersion -> $loaderVersion (agent fields untouched)"

            if ($legacySas) {
                try {
@@ -317,7 +500,7 @@ if ($DryRun) {
    Write-Host "AdminConfiguration.LatestBootstrapV2ScriptVersion = $scriptVersion"
 }

-# ------------------------------------------------------------------ 6. verify via alias
+# ------------------------------------------------------------------ 8. verify via alias
 if (-not $DryRun) {
    $pending = [System.Collections.ArrayList]::new()
    $publishSet | ForEach-Object { [void]$pending.Add($_) }
@@ -349,7 +532,8 @@ if ($env:GITHUB_STEP_SUMMARY) {
    $summary = @(
        "### Bootstrap scripts: $mode",
        '',
-        "Bootstrap script version: **$scriptVersion**",
+        "Loader script version: **$loaderVersion** | Bootstrap script version: **$scriptVersion**",
+        "Signed: **$(if ($SigningEnabled) { "yes, certificate '$CertificateName'" } else { 'NO (unsigned dry run)' })**",
        ''
    ) + ($publishSet | ForEach-Object { "- $($_.BlobName) -- sha256 $($_.Sha256)" })
    ($summary -join [Environment]::NewLine) | Out-File -FilePath $env:GITHUB_STEP_SUMMARY -Append -Encoding utf8
@@ -434,8 +434,16 @@ jobs:
            # to main, so a release lands a set that is consistent with what is already live
            # (dev render, version-bump guard, bootstrapVersion oracles, alias verification).
            # Runs AFTER version.json so its bootstrapVersion read sees this build's manifest.
+            # Same signing identity as the binaries above: the loader on every device
+            # verifies the publisher of the script it downloads, so the publisher refuses
+            # to upload unsigned scripts.
            ./.github/scripts/Publish-BootstrapScripts.ps1 `
-              -LegacySasToken '${{ secrets.AZURE_BLOB_AGENT_LEGACY_SAS_TOKEN }}'
+              -LegacySasToken '${{ secrets.AZURE_BLOB_AGENT_LEGACY_SAS_TOKEN }}' `
+              -SigningToken $env:CODE_SIGN_AKV_ACCESS_TOKEN `
+              -KeyVaultUrl $env:CODE_SIGN_KEY_VAULT_URL `
+              -CertificateName $env:CODE_SIGN_CERTIFICATE_NAME `
+              -TimestampUrl $env:CODE_SIGN_TIMESTAMP_URL `
+              -ExpectedPublisher $env:CODE_SIGN_EXPECTED_SUBJECT
          }

          # Update AdminConfiguration LatestAgentV2* -- ONLY on stable cutover. The hash-oracle
@@ -35,6 +35,16 @@ concurrency:
  group: agent-blob-publish
  cancel-in-progress: false

+# Authenticode for the customer scripts. Same identity and same repository variables as
+# build-agent.yml -- the loader on every device pins this publisher, so the two must not
+# drift apart.
+env:
+  CODE_SIGN_CLIENT_ID: ${{ vars.CODE_SIGN_CLIENT_ID }}
+  CODE_SIGN_CERTIFICATE_NAME: ${{ vars.CODE_SIGN_CERTIFICATE_NAME }}
+  CODE_SIGN_KEY_VAULT_URL: ${{ vars.CODE_SIGN_KEY_VAULT_URL }}
+  CODE_SIGN_EXPECTED_SUBJECT: ${{ vars.CODE_SIGN_EXPECTED_SUBJECT }}
+  CODE_SIGN_TIMESTAMP_URL: http://timestamp.acs.microsoft.com
+
 jobs:
  gates:
    uses: ./.github/workflows/bootstrap-script-gates.yml
@@ -46,6 +56,37 @@ jobs:
    steps:
      - uses: actions/checkout@v7

+      - name: Check code-signing configuration
+        shell: pwsh
+        run: |
+          foreach ($name in 'CODE_SIGN_CLIENT_ID', 'CODE_SIGN_CERTIFICATE_NAME', 'CODE_SIGN_KEY_VAULT_URL') {
+            if ([string]::IsNullOrWhiteSpace([Environment]::GetEnvironmentVariable($name))) {
+              throw "Repository variable $name is not set. Published customer scripts must be signed."
+            }
+          }
+
+      # First, and only to fetch the Key Vault token: azure/login sets the default az
+      # account and the storage login below has to be the one that stays. See D-223 --
+      # both federated credentials are bound to the ref, so this job must never carry a
+      # GitHub `environment:`.
+      - name: Login to Azure (code-signing identity)
+        uses: azure/login@7ddb5af1ef8758cf1353cf3b42f940aee27ba21c # v3
+        with:
+          client-id: ${{ env.CODE_SIGN_CLIENT_ID }}
+          tenant-id: ${{ secrets.AZURE_TENANT_ID }}
+          allow-no-subscriptions: true
+
+      - name: Acquire Key Vault token for signing
+        shell: pwsh
+        run: |
+          $ErrorActionPreference = 'Stop'
+          $token = az account get-access-token --scope https://vault.azure.net/.default --query accessToken --output tsv
+          if ($LASTEXITCODE -ne 0 -or [string]::IsNullOrWhiteSpace($token)) {
+            throw "Could not acquire a Key Vault token for the code-signing identity."
+          }
+          Write-Host "::add-mask::$token"
+          "CODE_SIGN_AKV_ACCESS_TOKEN=$token" | Out-File -FilePath $env:GITHUB_ENV -Encoding utf8 -Append
+
      # Authorizes the eu blob writes and the AdminConfiguration merge. The gates job above
      # runs the same publisher with -DryRun and deliberately without a login -- a dry run
      # must never need Azure credentials.
@@ -56,10 +97,38 @@ jobs:
          tenant-id: ${{ secrets.AZURE_TENANT_ID }}
          subscription-id: ${{ secrets.AZURE_SUBSCRIPTION_ID }}

+      # Version pinned so a new or compromised NuGet release cannot flow into signing
+      # unreviewed; roll-forward because the tool targets an older runtime than the SDK
+      # preinstalled on the runner.
+      - name: Install AzureSignTool
+        env:
+          DOTNET_ROLL_FORWARD: LatestMajor
+        run: dotnet tool install --no-cache --global AzureSignTool --version 7.0.1
+
      - name: Publish bootstrap + customer scripts
        shell: pwsh
+        env:
+          DOTNET_ROLL_FORWARD: LatestMajor
        run: |
          $dryRun = '${{ inputs.dry_run }}' -eq 'true'
          ./.github/scripts/Publish-BootstrapScripts.ps1 `
            -LegacySasToken '${{ secrets.AZURE_BLOB_AGENT_LEGACY_SAS_TOKEN }}' `
+            -SigningToken $env:CODE_SIGN_AKV_ACCESS_TOKEN `
+            -KeyVaultUrl $env:CODE_SIGN_KEY_VAULT_URL `
+            -CertificateName $env:CODE_SIGN_CERTIFICATE_NAME `
+            -TimestampUrl $env:CODE_SIGN_TIMESTAMP_URL `
+            -ExpectedPublisher $env:CODE_SIGN_EXPECTED_SUBJECT `
+            -SignedOutputDir "$env:RUNNER_TEMP/signed-scripts" `
            -DryRun:$dryRun
+
+      # The exact bytes that were (or, on a dry run, would have been) uploaded. A dry-run
+      # dispatch is therefore the way to inspect a signed script locally before it reaches
+      # a single customer. Kept on failure too: a failed alias verification is precisely
+      # when someone wants to look at the file.
+      - name: Upload signed scripts
+        if: always()
+        uses: actions/upload-artifact@v7
+        with:
+          name: signed-scripts
+          path: ${{ runner.temp }}/signed-scripts
+          if-no-files-found: ignore
@@ -0,0 +1,127 @@
+# Pester tests (Pester 5+) for the stage-1 loader Start-AutopilotMonitor.ps1.
+#
+# The script under test is dot-sourced; its entry guard prevents the loader from
+# executing, so loading it here is side-effect free. Network and signature checks
+# are mocked -- what is verified is the DECISION: what does the loader accept, what
+# does it refuse, and how often does it retry.
+#
+# Run under Windows PowerShell 5.1 to match the IME runtime:
+#   powershell.exe -NoProfile -Command "& { $c = New-PesterConfiguration; $c.Run.Path = 'scripts\Bootstrap'; $c.Output.Verbosity = 'Detailed'; Invoke-Pester -Configuration $c }"
+#
+# This file MUST remain pure ASCII (PS 5.1 reads BOM-less files as ANSI).
+
+BeforeAll {
+    . (Join-Path $PSScriptRoot 'Start-AutopilotMonitor.ps1')
+
+    function New-FakeSignature {
+        param([string]$Status, [string]$Subject)
+        $cert = if ($Subject) {
+            [pscustomobject]@{ Subject = $Subject; Thumbprint = '0123456789ABCDEF' }
+        } else { $null }
+        return [pscustomobject]@{ Status = $Status; SignerCertificate = $cert }
+    }
+}
+
+Describe 'Test-BootstrapSignature' {
+    BeforeEach {
+        Mock Write-Log { }
+    }
+
+    It 'accepts a valid signature from the expected publisher' {
+        Mock Get-AuthenticodeSignature { New-FakeSignature -Status 'Valid' -Subject 'CN=glueckkanja AG, O=glueckkanja AG, C=DE' }
+        Test-BootstrapSignature -Path 'TestDrive:\x.ps1' | Should -BeTrue
+    }
+
+    It 'refuses an unsigned script' {
+        Mock Get-AuthenticodeSignature { New-FakeSignature -Status 'NotSigned' -Subject $null }
+        Test-BootstrapSignature -Path 'TestDrive:\x.ps1' | Should -BeFalse
+    }
+
+    It 'refuses a tampered script (hash mismatch)' {
+        Mock Get-AuthenticodeSignature { New-FakeSignature -Status 'HashMismatch' -Subject 'CN=glueckkanja AG, O=glueckkanja AG, C=DE' }
+        Test-BootstrapSignature -Path 'TestDrive:\x.ps1' | Should -BeFalse
+    }
+
+    It 'refuses a signature whose chain does not validate' {
+        Mock Get-AuthenticodeSignature { New-FakeSignature -Status 'UnknownError' -Subject 'CN=glueckkanja AG, O=glueckkanja AG, C=DE' }
+        Test-BootstrapSignature -Path 'TestDrive:\x.ps1' | Should -BeFalse
+    }
+
+    # The whole point of the pinned publisher: a validly signed script from someone else
+    # is exactly what an attacker with any code-signing certificate can produce.
+    It 'refuses a valid signature from a different publisher' {
+        Mock Get-AuthenticodeSignature { New-FakeSignature -Status 'Valid' -Subject 'CN=Somebody Else, O=Somebody Else Ltd, C=US' }
+        Test-BootstrapSignature -Path 'TestDrive:\x.ps1' | Should -BeFalse
+    }
+
+    It 'refuses when the signature check itself fails' {
+        Mock Get-AuthenticodeSignature { throw 'file not found' }
+        Test-BootstrapSignature -Path 'TestDrive:\x.ps1' | Should -BeFalse
+    }
+}
+
+Describe 'Get-VerifiedBootstrapScript' {
+    BeforeEach {
+        Mock Write-Log { }
+        Mock Start-Sleep { }
+        Mock Invoke-WebRequest { }
+    }
+
+    It 'returns after the first attempt when the download verifies' {
+        Mock Test-BootstrapSignature { $true }
+        Get-VerifiedBootstrapScript -Url 'https://example.invalid/s.ps1' -Destination 'TestDrive:\s.ps1' | Should -BeTrue
+        Should -Invoke Invoke-WebRequest -Times 1 -Exactly
+    }
+
+    It 'gives up after three attempts when verification keeps failing' {
+        Mock Test-BootstrapSignature { $false }
+        Get-VerifiedBootstrapScript -Url 'https://example.invalid/s.ps1' -Destination 'TestDrive:\s.ps1' | Should -BeFalse
+        Should -Invoke Invoke-WebRequest -Times 3 -Exactly
+    }
+
+    # A truncated or proxy-mangled body fails verification, so the retry has to cover the
+    # download AND the check, not just the transport.
+    It 'retries a failed verification and accepts a later attempt' {
+        $script:calls = 0
+        Mock Test-BootstrapSignature { $script:calls++; return ($script:calls -ge 2) }
+        Get-VerifiedBootstrapScript -Url 'https://example.invalid/s.ps1' -Destination 'TestDrive:\s.ps1' | Should -BeTrue
+        Should -Invoke Invoke-WebRequest -Times 2 -Exactly
+    }
+
+    It 'retries a transport failure' {
+        $script:downloads = 0
+        Mock Invoke-WebRequest { $script:downloads++; if ($script:downloads -eq 1) { throw 'connection reset' } }
+        Mock Test-BootstrapSignature { $true }
+        Get-VerifiedBootstrapScript -Url 'https://example.invalid/s.ps1' -Destination 'TestDrive:\s.ps1' | Should -BeTrue
+        Should -Invoke Invoke-WebRequest -Times 2 -Exactly
+    }
+
+    It 'never executes anything when no attempt verifies' {
+        Mock Test-BootstrapSignature { $false }
+        Get-VerifiedBootstrapScript -Url 'https://example.invalid/s.ps1' -Destination 'TestDrive:\s.ps1' | Should -BeFalse
+    }
+}
+
+Describe 'publish contract' {
+    BeforeAll {
+        $script:loaderText = Get-Content (Join-Path $PSScriptRoot 'Start-AutopilotMonitor.ps1') -Raw
+    }
+
+    # Publish-BootstrapScripts.ps1 renders the -Dev loader by substituting this exact
+    # literal and fails the publish when it is gone. Catching that here means the PR fails
+    # instead of the publish.
+    It 'carries the dev-render anchor the publisher substitutes' {
+        $anchor = '$BootstrapUrl = "https://download.autopilotmonitor.com/agent/Install-AutopilotMonitor.ps1"'
+        $script:loaderText.Contains($anchor) | Should -BeTrue
+    }
+
+    # The publisher parses this to write version.json.loaderVersion and to run the
+    # version-bump guard.
+    It 'declares a parsable ScriptVersion' {
+        $script:loaderText -match '\$ScriptVersion\s*=\s*"([\d\.\-a-zA-Z]+)"' | Should -BeTrue
+    }
+
+    It 'pins the expected publisher by subject, not by thumbprint' {
+        $script:loaderText -match '\$ExpectedPublisher\s*=\s*"\*O=' | Should -BeTrue
+    }
+}
@@ -0,0 +1,197 @@
+<#
+.SYNOPSIS
+    Stage 1 of the Autopilot Monitor bootstrap: fetches the current installer and runs it.
+
+.DESCRIPTION
+    This is the file an administrator assigns in Intune. It carries no enrollment logic at
+    all: it downloads the published Install-AutopilotMonitor.ps1, proves that it was signed
+    by Autopilot Monitor, and runs it in this process.
+
+    Why two stages: the installer holds every guard, relax rule and download path, and those
+    change. Whoever assigns the installer directly has to replace their Intune copy each
+    time; whoever assigns this loader never does, because the part that changes lives on the
+    server. Assigning the installer directly stays supported and unchanged.
+
+    This file is deliberately boring. It is the one piece that cannot be fixed remotely, so
+    it does the least it can: download, verify, invoke, log.
+
+    Verification is by Authenticode publisher, not by hash. A hash oracle would have to be
+    fetched from the same host as the script itself, so it could not survive a compromise of
+    that host, while the expected publisher below travels with this file. It pins the
+    certificate SUBJECT and not a thumbprint, so a certificate renewal does not brick a
+    loader that is already deployed on devices.
+
+    Fail-soft: the loader always exits 0 and never throws into the caller. A device that
+    cannot reach the download endpoint is a device without monitoring, never a failed
+    enrollment step. Verification failures are the same: nothing runs, and the reason is in
+    the log. Refusing to execute unverified code as SYSTEM is the point of this file.
+
+    This file MUST remain pure ASCII (PS 5.1 reads BOM-less files as ANSI).
+
+.PARAMETER BootstrapUrl
+    Installer URL. Defaults to the published stable installer; the -Dev variant of this
+    loader is rendered from that default at publish time.
+
+.PARAMETER BootstrapArguments
+    Everything else is passed through to the installer unchanged, so any parameter the
+    installer accepts can be set here without this file knowing about it.
+
+.EXAMPLE
+    .\Start-AutopilotMonitor.ps1
+
+.EXAMPLE
+    .\Start-AutopilotMonitor.ps1 -MaxBootstrapWindowHours 24
+
+.NOTES
+    Author  : Oliver Kieselbach (autopilotmonitor.com)
+    Runtime : Windows PowerShell 5.1, SYSTEM context, during Autopilot enrollment
+
+.CHANGELOG
+    2026-09-08  v1.0  Initial version: two-stage bootstrap, publisher-pinned verification.
+#>
+
+[CmdletBinding()]
+param(
+    [Parameter(Mandatory = $false)]
+    [string]$BootstrapUrl = "https://download.autopilotmonitor.com/agent/Install-AutopilotMonitor.ps1",
+
+    [Parameter(Mandatory = $false, ValueFromRemainingArguments = $true)]
+    [string[]]$BootstrapArguments
+)
+
+# Script version (bump on meaningful changes; see .CHANGELOG above)
+$ScriptVersion = "1.0"
+
+# The publisher every downloaded stage-2 script must carry. A -like pattern on the subject,
+# NOT a thumbprint: certificates are renewed, deployed loaders are not.
+$ExpectedPublisher = "*O=glueckkanja AG*"
+
+$LoaderBasePath = "$env:ProgramData\AutopilotMonitor"
+$LoaderLogPath  = "$LoaderBasePath\Logs"
+$LogFile        = "$LoaderLogPath\bootstrap-loader.log"
+$BootstrapPath  = "$LoaderBasePath\Install-AutopilotMonitor.ps1"
+
+$DownloadAttempts = 3
+$RetryDelaySeconds = 10
+
+# Write-Host as well as the file: the Intune script output is what an administrator sees in
+# the portal, the file is what a support case reads.
+function Write-Log {
+    param([string]$Message)
+    $timestamp = Get-Date -Format "yyyy-MM-dd HH:mm:ss"
+    $logMessage = "[$timestamp] $Message"
+    Write-Host $logMessage
+    Add-Content -Path $LogFile -Value $logMessage -ErrorAction SilentlyContinue
+}
+
+# True only when the file is signed, the signature validates against the machine's trust
+# chain, and the signer is us. Any error is a false -- an unreadable signature is an
+# unverified script.
+function Test-BootstrapSignature {
+    param([string]$Path)
+
+    try {
+        $sig = Get-AuthenticodeSignature -FilePath $Path -ErrorAction Stop
+    }
+    catch {
+        Write-Log "Signature check failed to run: $($_.Exception.Message)"
+        return $false
+    }
+
+    if ($null -eq $sig) {
+        Write-Log "Signature check returned nothing."
+        return $false
+    }
+
+    $subject = if ($sig.SignerCertificate) { $sig.SignerCertificate.Subject } else { "<unsigned>" }
+    Write-Log "Signature status: $($sig.Status). Signer: $subject"
+
+    if ($sig.Status -ne 'Valid') {
+        Write-Log "REJECTED: expected signature status 'Valid'."
+        return $false
+    }
+    if ($subject -notlike $ExpectedPublisher) {
+        Write-Log "REJECTED: signer does not match the expected publisher."
+        return $false
+    }
+
+    Write-Log "Signature accepted (thumbprint $($sig.SignerCertificate.Thumbprint))."
+    return $true
+}
+
+# Downloads the installer and returns $true once a downloaded copy passes verification.
+# Verification lives inside the retry loop on purpose: a truncated or proxy-mangled body
+# fails the signature check, and that is worth another attempt.
+function Get-VerifiedBootstrapScript {
+    param([string]$Url, [string]$Destination)
+
+    for ($attempt = 1; $attempt -le $DownloadAttempts; $attempt++) {
+        try {
+            Write-Log "Download attempt $attempt/$DownloadAttempts from $Url"
+            Invoke-WebRequest -Uri $Url -OutFile $Destination -UseBasicParsing -TimeoutSec 60 -ErrorAction Stop
+
+            if (Test-BootstrapSignature -Path $Destination) {
+                return $true
+            }
+        }
+        catch {
+            Write-Log "Download attempt $attempt failed: $($_.Exception.Message)"
+        }
+
+        if ($attempt -lt $DownloadAttempts) {
+            Start-Sleep -Seconds $RetryDelaySeconds
+        }
+    }
+
+    return $false
+}
+
+# Main flow. Only invoked when the script is run directly (see entry guard at the bottom),
+# so the Pester suite can dot-source this file without bootstrapping anything.
+function Start-BootstrapLoader {
+    New-Item -ItemType Directory -Force -Path $LoaderLogPath -ErrorAction SilentlyContinue | Out-Null
+
+    Write-Log "=== Autopilot Monitor bootstrap loader v$ScriptVersion started (user=$env:USERNAME, pid=$PID) ==="
+
+    # PS 5.1 on an OOBE device still defaults to TLS 1.0 for this process.
+    try {
+        [Net.ServicePointManager]::SecurityProtocol = [Net.ServicePointManager]::SecurityProtocol -bor [Net.SecurityProtocolType]::Tls12
+    }
+    catch {
+        Write-Log "INFO: could not raise the TLS protocol: $($_.Exception.Message)"
+    }
+
+    if (-not (Get-VerifiedBootstrapScript -Url $BootstrapUrl -Destination $BootstrapPath)) {
+        Write-Log "No verified installer available after $DownloadAttempts attempt(s). Nothing was executed."
+        return
+    }
+
+    Write-Log "Executing $BootstrapPath"
+
+    # Same process, so the execution policy this loader runs under applies to stage 2 as
+    # well and no second policy decision can strand the installer. Splatting an array of
+    # remaining arguments keeps this file free of any knowledge about the installer's
+    # parameters.
+    $arguments = @()
+    if ($BootstrapArguments) { $arguments = $BootstrapArguments }
+
+    try {
+        & $BootstrapPath @arguments
+        Write-Log "Installer finished (exit code $LASTEXITCODE)."
+    }
+    catch {
+        Write-Log "Installer threw: $($_.Exception.Message)"
+    }
+}
+
+# Entry guard: dot-sourcing (Pester) loads the functions without running the loader.
+if ($MyInvocation.InvocationName -ne '.') {
+    try {
+        Start-BootstrapLoader
+    }
+    catch {
+        # Nothing above should throw; if it does, it must not become a failed Intune script.
+        Write-Log "Loader failed: $($_.Exception.Message)"
+    }
+    exit 0
+}