Add a tool to generate manifests for Apple MDM (#10959)

Related to #9459 this will allow us to host a `fleetd` metadata
alongside the installer that can be used by Apple's MDM
`InstallEnterpriseApplication`

server/mdm/apple/appmanifest/appmanifest.go

@@ -0,0 +1,39 @@
+// package appmanifest provides utilities for managing app manifest files
+// used by MDM InstallApplication commands.
+//
+// It's heavily based on the micromdm/mdm/appmanifest package but it uses
+// SHA256 as the hashing algorithm instead of MD5.
+package appmanifest
+
+import (
+	"crypto/sha256"
+	"fmt"
+	"io"
+
+	"github.com/micromdm/micromdm/mdm/appmanifest"
+)
+
+// Create builds an AppManifest using SHA256 checksums and the provided URL
+func Create(file io.Reader, url string) (*appmanifest.Manifest, error) {
+	hash := sha256.New()
+	if _, err := io.Copy(hash, file); err != nil {
+		return nil, err
+	}
+
+	sum := fmt.Sprintf("%x", hash.Sum(nil))
+
+	ast := appmanifest.Asset{
+		Kind:       "software-package",
+		SHA256Size: int64(hash.Size()),
+		SHA256s:    []string{sum},
+		URL:        url,
+	}
+
+	return &appmanifest.Manifest{
+		ManifestItems: []appmanifest.Item{
+			{
+				Assets: []appmanifest.Asset{ast},
+			},
+		},
+	}, nil
+}

server/mdm/apple/appmanifest/appmanifest_test.go

@@ -0,0 +1,52 @@
+package appmanifest
+
+import (
+	"errors"
+	"io"
+	"strings"
+	"testing"
+
+	"github.com/micromdm/micromdm/mdm/appmanifest"
+	"github.com/stretchr/testify/require"
+)
+
+var errTest = errors.New("test error")
+
+type alwaysFailReader struct{}
+
+func (alwaysFailReader) Read(p []byte) (n int, err error) {
+	return 0, errTest
+}
+
+func TestCreate(t *testing.T) {
+	url := "https://test.example.com"
+
+	cases := []struct {
+		in  io.Reader
+		out *appmanifest.Manifest
+		err error
+	}{
+		{
+			in: strings.NewReader("foo"),
+			out: &appmanifest.Manifest{
+				ManifestItems: []appmanifest.Item{{Assets: []appmanifest.Asset{{
+					Kind:       "software-package",
+					SHA256Size: 32,
+					SHA256s:    []string{"2c26b46b68ffc68ff99b453c1d30413413422d706483bfa0f98a5e886266e7ae"},
+					URL:        "https://test.example.com",
+				}}}}},
+			err: nil,
+		},
+		{
+			in:  alwaysFailReader{},
+			out: nil,
+			err: errTest,
+		},
+	}
+
+	for _, c := range cases {
+		m, err := Create(c.in, url)
+		require.Equal(t, c.out, m)
+		require.Equal(t, c.err, err)
+	}
+}

tools/mdm/apple/appmanifest/README.md

@@ -0,0 +1,36 @@
+## appmanifest
+
+`appmanifest` is a tool that outputs to stdout a valid XML manifest that can be used by the MDM `InstallEnterpriseApplication` command to install a package.
+
+```
+$ go run tools/mdm/apple/appmanifest/main.go --help
+Usage of appmanifest:
+  -pkg-file string
+    	Path to a .pkg file
+  -pkg-url string
+    	URL where the package will be served
+```
+
+### Example workflow
+
+1. Create a fleetd installer
+
+```
+fleetctl package --type=pkg --fleet-desktop
+```
+
+2. Sign the installer so it can be installed via MDM
+
+```
+productsign --sign "Developer ID Installer: $DEVID_INFO" fleet-osquery.pkg fleetd-base.pkg
+```
+
+3. Run `appmanifest`
+
+```
+$ go run tools/mdm/apple/appmanifest/main.go \
+    -pkg-file fleetd-base.pkg \
+    -pkg-url $YOUR_URL > fleetd-base-manifest.plist
+```
+
+4. Upload `fleetd-base.pkg` to `$YOUR_URL` and `fleetd-base-manifest.plist` to a publicly accessible location.

tools/mdm/apple/appmanifest/main.go

@@ -0,0 +1,43 @@
+// Command appmanifest takes a .pkg file and outputs an XML manifest for it
+package main
+
+import (
+	"bytes"
+	"flag"
+	"fmt"
+	"log"
+	"os"
+
+	"github.com/fleetdm/fleet/v4/server/mdm/apple/appmanifest"
+	"github.com/groob/plist"
+)
+
+func main() {
+	pkgFile := flag.String("pkg-file", "", "Path to a .pkg file")
+	pkgURL := flag.String("pkg-url", "", "URL where the package will be served")
+	flag.Parse()
+
+	if *pkgFile == "" || *pkgURL == "" {
+		log.Fatal("both --pkg-file and --pkg-url must be provided")
+	}
+
+	fp, err := os.Open(*pkgFile)
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer fp.Close()
+
+	m, err := appmanifest.Create(fp, *pkgURL)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	var buf bytes.Buffer
+	enc := plist.NewEncoder(&buf)
+	enc.Indent("  ")
+	if err := enc.Encode(m); err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Println(buf.String())
+}