While it's 100% possible for a server with plugins enabled to control who can use /checkspawn, we want to be able to run it in singleplayer for players who don't have cheats enabled.

For some reason when I was entering the commands in the Quest book, they didn't run for the player. I checked 'run as player' and it worked, but it turns out that that only works if the player has cheats enabled; it runs into the same permission errors as any normal singleplayer would.

I've been wondering for awhile whether the quest book would just pick a random player close to start when typing a command like execute @p, but according to this (FTBTeam/FTB-Mods-Issues#716) what actually happens is there's some substitution internal to FTBQuests that replaced @p with the name of the player receiving a reward. I should try again to fix the quest to run for players regardless of whether they have cheats enabled.

According to the net, /execute as @p does circumvent the normal permissions problems.

Unfortunately, if you /execute as @p, the output is eaten and never seen by the player. You can test this by putting the code in a command block.

I tried to take a single player world without cheats enabled, put the player briefly in creative mode, run the command for them using the 'run as player' option in FTBQuests, and take them out of creative mode again immediately. However, nothing happened.

I have marked this as wontfix.