Using SSL client certs with Perl’s LWP::UserAgent

by on Mar.29, 2013, under Programming, Perl

I recently needed to authenticate to a remote API using an SSL client certificate, and had a bit of trouble getting LWP::UserAgent to work with it.

The examples I found which looked like they should work involved e.g.:

use LWP::UserAgent;
my $ua = LWP::UserAgent->new(
    ssl_opts => {
        SSL_use_cert => 1,
        SSL_cert_file   => "/path/to/clientcert.crt",
        SSL_key_file    => "/path/to/privatekey.key",

However, that didn’t work; changing the paths to the cert/key to non-existent files didn’t cause any difference, so I suspected that those options were actually being ignored.

After a fair bit of digging, the option I found that actually worked was loading Net::SSL first, to make LWP use Net::SSLeay, and setting env vars to the client cert to use:

use Net::SSL;
use LWP::UserAgent;
$ENV{HTTPS_CERT_FILE} = "/path/to/clientcert.crt";
$ENV{HTTPS_KEY_FILE}  = "/path/to/privatekey.key";
my $ua = LWP::UserAgent->new();

This, to me, is pretty icky – I’d much rather pass config to affect just that single LWP object. However, it gets it working.

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