lost user password, disabled root login. no sudo access

The problem is you are prompted for the new password AGAIN, and if you fail, the prompt exists.

Its hard trying it by hand so you can try this code in developer tools :

var sendString = (function(rfb, force, sendDelay) { 
  sendDelay = sendDelay || 25;
  var _q = [];
  var _qStart = function() {
    var chr = _q.shift();
    if (chr) {
      rfb.sendKey(chr);
      setTimeout(_qStart, sendDelay);
    }
  };
  var _qStop = function() { _q.length = 0; };
  var fn = function sendString(str) {
    _qStop();
    str = str || '';
    var chr;
    for (var i=0; i < str.length; i++) {
      chr = str[i].charCodeAt();
      _q.push(chr);
    }
    _qStart();
  };
  if (rfb.sendString && true !== force) {
    console.warn('rfb.sendString not installed because it already exists.  Use force if you\'d like');
  }
  else {
    rfb.sendString = fn;
  }
  return fn;
})(rfb);

then send text with sendString(‘yourletters’);