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

IO::Socket::SSL::set_defaults(passwd_cb => sub { "passwordvaluehere" }); 
$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_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