Lock Screen widgets in Android 4.4 KitKat is not enabled by default, and since the new HTC One M8 runs Android KitKat you need to do as follows to enable lock screen widgets and open your favorite widgets right from the lock screen:
1. Open Settings app
2. Under Personal settings, open Security.
3. make sure to mark the "Enable lock screen widgets" option
Tip: To add widgets on lock screen, you just need to swipe right from the corner right of the lock screen and use the Plus icon to add widgets.