how to solve this? I don't know how to install Mozilla::CA module on OS X.

➜  ~ efetch -db nuccore -id AF086833 -format gb  > AF086833.gb
500 Can't verify SSL peers without knowing which Certificate Authorities to trust
No do_post output returned from 'https://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=nuccore&id=AF086833&rettype=gb&retmode=text&edirect=6.00&tool=edirect&email=hudonghui@h48.144.226.10.102171.vlan.kuins.net'
Result of do_post http request is
$VAR1 = bless( {
                 '_rc' => 500,
                 '_msg' => 'Can\'t verify SSL peers without knowing which Certificate Authorities to trust',
                 '_headers' => bless( {
                                        'client-warning' => 'Internal response',
                                        'content-type' => 'text/plain',
                                        '::std_case' => {
                                                          'client-date' => 'Client-Date',
                                                          'client-warning' => 'Client-Warning'
                                                        },
                                        'client-date' => 'Mon, 01 May 2017 05:34:27 GMT'
                                      }, 'HTTP::Headers' ),
                 '_content' => 'Can\'t verify SSL peers without knowing which Certificate Authorities to trust

This problem can be fixed by either setting the PERL_LWP_SSL_CA_FILE
envirionment variable or by installing the Mozilla::CA module.

To disable verification of SSL peers set the PERL_LWP_SSL_VERIFY_HOSTNAME
envirionment variable to 0.  If you do this you can\'t be sure that you
communicate with the expected peer.
',
                 '_request' => bless( {
                                        '_uri' => bless( do{\(my $o = 'https://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi')}, 'URI::https' ),
                                        '_content' => 'db=nuccore&id=AF086833&rettype=gb&retmode=text&edirect=6.00&tool=edirect&email=hudonghui@h48.144.226.10.102171.vlan.kuins.net',
                                        '_method' => 'POST',
                                        '_headers' => bless( {
                                                               'user-agent' => 'libwww-perl/6.05',
                                                               'content-type' => 'application/x-www-form-urlencoded'
                                                             }, 'HTTP::Headers' )
                                      }, 'HTTP::Request' )
               }, 'HTTP::Response' );