Implements windows loading of MDM policy

client/mdm/policy_windows.go

@@ -2,9 +2,110 @@
 
 package mdm
 
-// loadPlatformPolicy reads the MDM configuration from the Windows registry
-// under HKLM\Software\Policies\NetBird. Phase 1 ships a stub; the real
-// reader lands in Phase 3.
+import (
+	"errors"
+	"fmt"
+	"strings"
+
+	log "github.com/sirupsen/logrus"
+	"golang.org/x/sys/windows/registry"
+)
+
+// canonicalKey maps the lowercase form of a registry value name to its
+// canonical mdm.Key* name. Admins commonly write PascalCase value names in
+// ADMX / Group Policy ("ManagementURL"), the iOS/AppConfig convention is
+// camelCase ("managementURL"); both must resolve to the same Policy lookup.
+var canonicalKey = func() map[string]string {
+	m := make(map[string]string, len(AllKeys))
+	for _, k := range AllKeys {
+		m[strings.ToLower(k)] = k
+	}
+	return m
+}()
+
+// policyRegistryPath is the well-known MDM policy registry key for NetBird.
+// Admins push values here through Group Policy, Intune ADMX ingestion, an
+// Intune custom Registry CSP profile, or `reg add` during MSI deployment.
+// Listed in the project's docs/mdm/netbird.admx schema.
+const policyRegistryPath = `Software\Policies\NetBird`
+
+// loadPlatformPolicy reads the MDM-managed configuration from the Windows
+// registry under HKLM\Software\Policies\NetBird. Returns:
+//   - (nil, nil)  when the key is absent (device not MDM-enrolled for NetBird)
+//   - (map, nil)  with N entries when N managed values are set (N may be 0)
+//   - (nil, err)  on any other registry error
+//
+// Type coercion of registry value types into the Policy map:
+//   - REG_SZ        -> string
+//   - REG_EXPAND_SZ -> string (expanded by the registry API)
+//   - REG_DWORD     -> int64 (caller's GetBool handles 0/!=0 coercion)
+//   - REG_QWORD     -> int64
+//   - REG_MULTI_SZ  -> []string
+//
+// Unsupported value types (REG_BINARY, REG_NONE, ...) are skipped with a
+// warning so a malformed deployment does not block startup.
 func loadPlatformPolicy() (map[string]any, error) {
-	return nil, nil
+	k, err := registry.OpenKey(registry.LOCAL_MACHINE, policyRegistryPath, registry.QUERY_VALUE)
+	if err != nil {
+		if errors.Is(err, registry.ErrNotExist) {
+			// Not enrolled. Caller treats nil as "no MDM source present".
+			return nil, nil
+		}
+		return nil, fmt.Errorf("open %s: %w", policyRegistryPath, err)
+	}
+	defer func() {
+		if closeErr := k.Close(); closeErr != nil {
+			log.Warnf("mdm: close registry key %s: %v", policyRegistryPath, closeErr)
+		}
+	}()
+
+	names, err := k.ReadValueNames(-1)
+	if err != nil {
+		return nil, fmt.Errorf("enumerate values of %s: %w", policyRegistryPath, err)
+	}
+
+	out := make(map[string]any, len(names))
+	for _, name := range names {
+		// Canonicalize the registry value name against the known MDM key
+		// set so Policy.HasKey lookups (which use the canonical names)
+		// succeed regardless of the casing used by the admin's ADMX or
+		// `reg add` command.
+		canonical, known := canonicalKey[strings.ToLower(name)]
+		if !known {
+			log.Warnf("mdm: ignoring unknown registry value %s\\%s", policyRegistryPath, name)
+			continue
+		}
+
+		_, valType, err := k.GetValue(name, nil)
+		if err != nil {
+			log.Warnf("mdm: stat %s\\%s: %v", policyRegistryPath, name, err)
+			continue
+		}
+		switch valType {
+		case registry.SZ, registry.EXPAND_SZ:
+			if v, _, err := k.GetStringValue(name); err == nil {
+				out[canonical] = v
+			} else {
+				log.Warnf("mdm: read string %s\\%s: %v", policyRegistryPath, name, err)
+			}
+		case registry.DWORD, registry.QWORD:
+			if v, _, err := k.GetIntegerValue(name); err == nil {
+				// uint64 from the registry API; Policy.GetBool / GetInt
+				// helpers consume int64, so narrow safely.
+				out[canonical] = int64(v)
+			} else {
+				log.Warnf("mdm: read int %s\\%s: %v", policyRegistryPath, name, err)
+			}
+		case registry.MULTI_SZ:
+			if v, _, err := k.GetStringsValue(name); err == nil {
+				out[canonical] = v
+			} else {
+				log.Warnf("mdm: read multi-string %s\\%s: %v", policyRegistryPath, name, err)
+			}
+		default:
+			log.Warnf("mdm: ignoring unsupported registry value type %d at %s\\%s",
+				valType, policyRegistryPath, name)
+		}
+	}
+	return out, nil
 }