node pcsclite read card certificate

Question

I've got what I thought would be a fairly simple app, in which I'm on debian Linux (doesn't have to be cross-platform) and I need to read a smart card to get the user's UID / LDAP username, which should be stored in the certificate that's on the card.

I did this kind of thing successfully on Windows using powershell, following something like this: View All Certificates On Smart Card

But I'm struggling to do the same in node. I've so far pulled in pcsclite, used the node-pcsclite example code to verify the environment works. Here's the code that I'm successfully running:

#!/usr/bin/env node

var pcsc = require('../index');

var pcsc = pcsc();
pcsc.on('reader', function(reader) {

    console.log('New reader detected', reader.name);

    reader.on('error', function(err) {
        console.log('Error(', this.name, '):', err.message);
    });

    reader.on('status', function(status) {
        console.log('Status(', this.name, '):', status);
        /* check what has changed */
        var changes = this.state ^ status.state;
        if (changes) {
            if ((changes & this.SCARD_STATE_EMPTY) && (status.state & this.SCARD_STATE_EMPTY)) {
                console.log("card removed");/* card removed */
                reader.disconnect(reader.SCARD_LEAVE_CARD, function(err) {
                    if (err) {
                        console.log(err);
                    } else {
                        console.log('Disconnected');
                    }
                });
            } else if ((changes & this.SCARD_STATE_PRESENT) && (status.state & this.SCARD_STATE_PRESENT)) {
                console.log("card inserted");/* card inserted */
                reader.connect({ share_mode : this.SCARD_SHARE_SHARED }, function(err, protocol) {
                    if (err) {
                        console.log(err);
                    } else {
                        console.log('Protocol(', reader.name, '):', protocol);
                        reader.transmit(new Buffer([0x00, 0xB0, 0x00, 0x00, 0x20]), 40, protocol, function(err, data) {
                            if (err) {
                                console.log(err);
                            } else {
                                console.log('Data received', data);
                                reader.close();
                                pcsc.close();
                            }
                        });
                    }
                });
            }
        }
    });

    reader.on('end', function() {
        console.log('Reader',  this.name, 'removed');
    });
});

pcsc.on('error', function(err) {
    console.log('PCSC error', err.message);
});

So this works exactly as documented, no issues. If I insert my smart card I get the expected output.

What I'm not grokking is what exactly the 'data' in the .transmit() callback represents. It's a buffer, an array of hex numbers (it looks like), but I'm not clear on how I'd go about turning that into something readable that I can compare for access approval (for this app, I just want to compare the user's UID against a whitelist).

I've tried reading the pcsc-lite docs and the PC/SC standard, but the actual meaning of the data is pretty opaque to me so far.

Of course I've tried a few simple things like calling data.toString() with various encodings, without success thus far.

Any thoughts on how I can take what I've gotten so far from node-pcsclite and harvest any kind of human-readable information for use?