I think that was meant metaphorically- I can't imagine that there were such things as "keys" to the maginot line that could be used even if the defenders inside wanted to stop you, and it is furthermore unlikely that Alsatian civilians would have such access.

The Germans, after surrounding the line, did try a few attacks, but mostly just kept it contained and diverted their efforts elsewhere. After Weygand's surrender, large portions of the line had not seen any action, and therefore did technically surrender without a fight. Not sure if that is what you're looking for though.