CentOS 6 vs CPAN and Let's Encrypt

Here is the magic to get CPAN CLI to work with https.

# cpan

cpan[1]> o conf urllist https://www.perl.com/CPAN
Please use 'o conf commit' to make the config permanent!

cpan[2]> o conf urllist                                 
    urllist           
        0 [https://www.perl.com/CPAN]
Type 'o conf' to view all configuration items

cpan[3]> o conf commit
commit: wrote '/usr/share/perl5/CPAN/Config.pm'

If it is giving you problems with SSL certificat verification, then you have to upgrade openssl, ca-certificate to the latest version. Perl also maintains it's own SSL certificates in Mozilla::CA, so you might need to do

SSL_CERT_FILE=/etc/pki/ca-trust/extracted/pem/tls-ca-bundle.pem cpan Mozilla::CA