use LWP::UserAgent;
use Data::Dumper;
use IO::Socket::SSL qw(debug4);

$endpoint = ‘https://omit/commotest';

$ua = LWP::UserAgent->new;
$ua->ssl_opts(SSL_cert_file => 'der.cer');
$ua->ssl_opts(SSL_key_file => 'privatekey.pfx');
$ua->ssl_opts(SSL_passwd_cb => sub { return "passwordvaluehere"; } );
$ua->ssl_opts(SSL_use_cert => '1');

$response = $ua->get($endpoint);           

if ($response->is_success) 
 {  print Dumper $response; }
else { print "Error: " . $response->status_line, "\n"; }

##</code><code>##

DEBUG: .../IO/Socket/SSL.pm:2411: Failed to load key from file (no PEM or DER)
SSL error:  4824: 1 - error:0606F076:digital envelope routines:EVP_PKCS82PKEY:unsupported private key algorithm
SSL error:  4824: 2 - error:140B000D:SSL routines:SSL_CTX_use_PrivateKey_file:ASN1 lib