"I don't think I am"

All the evidence points to this. cpanm is just a perl module, installed to a specific perl, in this case v5.18 which you installed via perlbrew. I'll take a look at the next issue when I get to work.

Update: I may not get round to looking at this in any detail today but you require credentials.pl, which does not return true. From the linked docs:

"The file must return true as the last statement to indicate successful execution of any initialization code, so it's customary to end such a file with 1; unless you're sure it'll return true otherwise. But it's better just to put the 1; , in case you add more statements."