A Node.js app to use NFC to unlock/lock Ubuntu.

unlock.js

var http = require('http'),
    url = require('url'),
    exec = require('child_process').exec;

var locked = false;

var app = http.createServer(function(request, response) {

  var url_parts = url.parse(request.url, true);
  var path = url_parts.pathname.replace(/^\/|\/$/g, '');

  if (request.method == 'GET') {

    if (path == '') {
      var get_data = url_parts.query;
      response.writeHead(200, {'Content-Type': 'text/plain'});

      if (get_data.secret == 'secret') {

        console.log('Access Granted');
        response.end('Access Granted');

        exec(__dirname + '/unlock.sh ' + locked, function(error, stdout, stderr) {
          var out = error ? stderr : stdout;
          console.log(out);
          locked = !locked;
        });

      } else {

        console.log('Access Denied');
        response.end('Access Denied');

      }

    }

  }
}).listen(6001);

console.log('Server running at localhost:6001');

unlock.sh

#!/bin/bash

export XAUTHORITY=/home/$USER/.Xauthority
export DISPLAY=:0.0

case "$1" in
    true)
        echo "Unlocking"
        loginctl unlock-sessions
        xset dpms force on
        xset s reset
        ;;
    false)
        echo "Locking"
        loginctl lock-sessions
        xset dpms force off
        ;;
esac

Note: unlock.js must be run as root because loginctl requires root to run.

You can set up a script run as root which monitors the status of a file and locks/unlocks accordingly. This would require modifying unlock.js to set the state of the file and unlock.sh to monitor it, but you would have to then run two scripts instead of just the server.