This is a different request from the capturing of input keys and combinations such as the Windows Key and Alt+Tab. The issue with Ctrl+Alt+Del is that it is an interrupt, so it cannot be captured and forwarded. Although the web UI provides clickable shortcuts for Ctrl+Alt+Del and other key combinations, it is inconvenient and slow, especially when it must be frequently pressed (lock screen) and the toolbar is collapsed.
Microsoft solved the issue of sending Ctrl+Alt+Del to the remote system with the Remote Desktop client by capturing the combination of Ctrl+Alt+End. When that combination is pressed by the user, Ctrl+Alt+Del is instead sent to the target.
Similarly, the GLKVM client should use Ctrl+Alt+End as a "hotkey" for Ctrl+Alt+Del. This would be great by its own, but it would be even better if the key shortcuts in the UI could provide user customization to activate the macros with user-defined hotkeys.