util/syspolicy: add auto exit node related keys (#11996)

Updates tailscale/corp#19681

Signed-off-by: Claire Wang <claire@tailscale.com>

util/syspolicy/syspolicy_test.go

@@ -5,6 +5,7 @@ package syspolicy
 
 import (
 	"errors"
+	"slices"
 	"testing"
 	"time"
 )
@@ -408,6 +409,63 @@ func TestGetDuration(t *testing.T) {
 	}
 }
 
+func TestGetStringArray(t *testing.T) {
+	tests := []struct {
+		name         string
+		key          Key
+		handlerValue []string
+		handlerError error
+		defaultValue []string
+		wantValue    []string
+		wantError    error
+	}{
+		{
+			name:         "read existing value",
+			key:          AllowedSuggestedExitNodes,
+			handlerValue: []string{"foo", "bar"},
+			wantValue:    []string{"foo", "bar"},
+		},
+		{
+			name:         "read non-existing value",
+			key:          AllowedSuggestedExitNodes,
+			handlerError: ErrNoSuchKey,
+			wantError:    nil,
+		},
+		{
+			name:         "read non-existing value, non nil default",
+			key:          AllowedSuggestedExitNodes,
+			handlerError: ErrNoSuchKey,
+			defaultValue: []string{"foo", "bar"},
+			wantValue:    []string{"foo", "bar"},
+			wantError:    nil,
+		},
+		{
+			name:         "reading value returns other error",
+			key:          AllowedSuggestedExitNodes,
+			handlerError: someOtherError,
+			wantError:    someOtherError,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			SetHandlerForTest(t, &testHandler{
+				t:    t,
+				key:  tt.key,
+				sArr: tt.handlerValue,
+				err:  tt.handlerError,
+			})
+			value, err := GetStringArray(tt.key, tt.defaultValue)
+			if err != tt.wantError {
+				t.Errorf("err=%q, want %q", err, tt.wantError)
+			}
+			if !slices.Equal(tt.wantValue, value) {
+				t.Errorf("value=%v, want %v", value, tt.wantValue)
+			}
+		})
+	}
+}
+
 func TestSelectControlURL(t *testing.T) {
 	tests := []struct {
 		reg, disk, want string