This is the chest locking mod. Once you place a chest down, it automatically locks with only you having permission to open it.
You change the settings and permissions of it by running the following commands and then punching the chest you want to change.
Set
/htm set PUBLIC: Allows everyone to access the container
/htm set PRIVATE: Allows only the owner and those with permissions to access the container
/htm set KEY: Allows only those with a key to access the container
Trust
/htm trust player [global]: Allows a player to access that container if private
/htm untrust player [global]: Revokes a player’s access to the container
Ownership
/htm remove: Removes all protections from a container
/htm transfer player: Transfers ownership to another player
Additional Commands
/htm flag: Checks the flags of a specific container. Left click on the container after running this command to check
/htm persist: Toggles persist mode, which allows you to continue executing the same action without typing the command again