Shiny user fingerprint (md5 hash of browser characteristics) and ip address demo. The .R files are in the working directory ("./"), the .js files must be placed in ./www/js/ to be accessible. I wrote the R code, which I will release under the same WTF license as the jqfp.js library is released under.

jqfp.js

// Browser fingerprinting is a technique to "mark" anonymous users using JS
// (or other things).  To build an "identity" of sorts the browser is queried
// for a list of its plugins, the screen size and several other things, then
// hashes them.  The idea is that these bits of information produce an unique
// "fingerprint" of sorts; the more elaborate the list of data points is, the
// more unique this fingerprint becomes.  And you wouldn't even need to set a
// cookie to recognize this user when she visits again.
//
// For more information on this topic consult
// [Ars Technica](http://arstechnica.com/tech-policy/news/2010/05/how-your-web-browser-rats-you-out-online.ars)
// or the [EFF](http://panopticlick.eff.org/).  There is a lot of potential
// for undesirable shenanigans, and I strictly oppose using this technique for
// marketing and ad-related tracking purposes.
//
// Anyways, I needed a really simple fingerprinting library, so I wrote a
// quick and dirty jQuery plugin.  This is by no means a complete and
// watertight implementation -- it is merely the scratch for a particular itch
// I was having.  YMMV.
//
// This library was written by Carlo Zottmann, carlo@municode.de, has its home
// on [Github](http://github.com/carlo/jquery-browser-fingerprint) and is
// WTF-licensed (see LICENSE.txt).

( function($) {

  // Calling `jQuery.fingerprint()` will return an MD5 hash, i.e. said
  // fingerprint.

  $.fingerprint = function() {

    // This function, `_raw()`, uses several browser details which are
    // available to JS here to build a string, namely...
    //
    // * the user agent
    // * screen size
    // * color depth
    // * the timezone offset
    // * sessionStorage support
    // * localStorage support
    // * the list of all installed plugins (we're using their names,
    //    descriptions, mime types and file name extensions here)
    function _raw() {
      // That string is the return value.
      return [
        navigator.userAgent,
        [ screen.height, screen.width, screen.colorDepth ].join("x"),
        ( new Date() ).getTimezoneOffset(),
        !!window.sessionStorage,
        !!window.localStorage,
        $.map( navigator.plugins, function(p) {
          return [
            p.name,
            p.description,
            $.map( p, function(mt) {
              return [ mt.type, mt.suffixes ].join("~");
            }).join(",")
          ].join("::");
        }).join(";")
      ].join("###");
    }

    // `_md5()` computes a MD5 hash using [md5-js](http://github.com/wbond/md5-js/).
    function _md5() {
      if ( typeof window.md5 === "function" ) {
        // The return value is the hashed fingerprint string.
        return md5( _raw() );
      }
      else {
        // If `window.md5()` isn't available, an error is thrown.
        throw "md5 unavailable, please get it from http://github.com/wbond/md5-js/";
      }
    }

    // And, since I'm lazy, calling `$.fingerprint()` will return the hash
    // right away, without the need for any other calls.
    return _md5();
  }

})(jQuery);

md5.js

/*!
 * Joseph Myer's md5() algorithm wrapped in a self-invoked function to prevent
 * global namespace polution, modified to hash unicode characters as UTF-8.
 *  
 * Copyright 1999-2010, Joseph Myers, Paul Johnston, Greg Holt, Will Bond <will@wbond.net>
 * http://www.myersdaily.org/joseph/javascript/md5-text.html
 * http://pajhome.org.uk/crypt/md5
 * 
 * Released under the BSD license
 * http://www.opensource.org/licenses/bsd-license
 */
(function() {
	function md5cycle(x, k) {
		var a = x[0], b = x[1], c = x[2], d = x[3];

		a = ff(a, b, c, d, k[0], 7, -680876936);
		d = ff(d, a, b, c, k[1], 12, -389564586);
		c = ff(c, d, a, b, k[2], 17, 606105819);
		b = ff(b, c, d, a, k[3], 22, -1044525330);
		a = ff(a, b, c, d, k[4], 7, -176418897);
		d = ff(d, a, b, c, k[5], 12, 1200080426);
		c = ff(c, d, a, b, k[6], 17, -1473231341);
		b = ff(b, c, d, a, k[7], 22, -45705983);
		a = ff(a, b, c, d, k[8], 7, 1770035416);
		d = ff(d, a, b, c, k[9], 12, -1958414417);
		c = ff(c, d, a, b, k[10], 17, -42063);
		b = ff(b, c, d, a, k[11], 22, -1990404162);
		a = ff(a, b, c, d, k[12], 7, 1804603682);
		d = ff(d, a, b, c, k[13], 12, -40341101);
		c = ff(c, d, a, b, k[14], 17, -1502002290);
		b = ff(b, c, d, a, k[15], 22, 1236535329);

		a = gg(a, b, c, d, k[1], 5, -165796510);
		d = gg(d, a, b, c, k[6], 9, -1069501632);
		c = gg(c, d, a, b, k[11], 14, 643717713);
		b = gg(b, c, d, a, k[0], 20, -373897302);
		a = gg(a, b, c, d, k[5], 5, -701558691);
		d = gg(d, a, b, c, k[10], 9, 38016083);
		c = gg(c, d, a, b, k[15], 14, -660478335);
		b = gg(b, c, d, a, k[4], 20, -405537848);
		a = gg(a, b, c, d, k[9], 5, 568446438);
		d = gg(d, a, b, c, k[14], 9, -1019803690);
		c = gg(c, d, a, b, k[3], 14, -187363961);
		b = gg(b, c, d, a, k[8], 20, 1163531501);
		a = gg(a, b, c, d, k[13], 5, -1444681467);
		d = gg(d, a, b, c, k[2], 9, -51403784);
		c = gg(c, d, a, b, k[7], 14, 1735328473);
		b = gg(b, c, d, a, k[12], 20, -1926607734);

		a = hh(a, b, c, d, k[5], 4, -378558);
		d = hh(d, a, b, c, k[8], 11, -2022574463);
		c = hh(c, d, a, b, k[11], 16, 1839030562);
		b = hh(b, c, d, a, k[14], 23, -35309556);
		a = hh(a, b, c, d, k[1], 4, -1530992060);
		d = hh(d, a, b, c, k[4], 11, 1272893353);
		c = hh(c, d, a, b, k[7], 16, -155497632);
		b = hh(b, c, d, a, k[10], 23, -1094730640);
		a = hh(a, b, c, d, k[13], 4, 681279174);
		d = hh(d, a, b, c, k[0], 11, -358537222);
		c = hh(c, d, a, b, k[3], 16, -722521979);
		b = hh(b, c, d, a, k[6], 23, 76029189);
		a = hh(a, b, c, d, k[9], 4, -640364487);
		d = hh(d, a, b, c, k[12], 11, -421815835);
		c = hh(c, d, a, b, k[15], 16, 530742520);
		b = hh(b, c, d, a, k[2], 23, -995338651);

		a = ii(a, b, c, d, k[0], 6, -198630844);
		d = ii(d, a, b, c, k[7], 10, 1126891415);
		c = ii(c, d, a, b, k[14], 15, -1416354905);
		b = ii(b, c, d, a, k[5], 21, -57434055);
		a = ii(a, b, c, d, k[12], 6, 1700485571);
		d = ii(d, a, b, c, k[3], 10, -1894986606);
		c = ii(c, d, a, b, k[10], 15, -1051523);
		b = ii(b, c, d, a, k[1], 21, -2054922799);
		a = ii(a, b, c, d, k[8], 6, 1873313359);
		d = ii(d, a, b, c, k[15], 10, -30611744);
		c = ii(c, d, a, b, k[6], 15, -1560198380);
		b = ii(b, c, d, a, k[13], 21, 1309151649);
		a = ii(a, b, c, d, k[4], 6, -145523070);
		d = ii(d, a, b, c, k[11], 10, -1120210379);
		c = ii(c, d, a, b, k[2], 15, 718787259);
		b = ii(b, c, d, a, k[9], 21, -343485551);

		x[0] = add32(a, x[0]);
		x[1] = add32(b, x[1]);
		x[2] = add32(c, x[2]);
		x[3] = add32(d, x[3]);
	}

	function cmn(q, a, b, x, s, t) {
		a = add32(add32(a, q), add32(x, t));
		return add32((a << s) | (a >>> (32 - s)), b);
	}

	function ff(a, b, c, d, x, s, t) {
		return cmn((b & c) | ((~b) & d), a, b, x, s, t);
	}

	function gg(a, b, c, d, x, s, t) {
		return cmn((b & d) | (c & (~d)), a, b, x, s, t);
	}

	function hh(a, b, c, d, x, s, t) {
		return cmn(b ^ c ^ d, a, b, x, s, t);
	}

	function ii(a, b, c, d, x, s, t) {
		return cmn(c ^ (b | (~d)), a, b, x, s, t);
	}

	function md51(s) {
		// Converts the string to UTF-8 "bytes" when necessary
		if (/[\x80-\xFF]/.test(s)) {
			s = unescape(encodeURI(s));
		}
		txt = '';
		var n = s.length, state = [1732584193, -271733879, -1732584194, 271733878], i;
		for (i = 64; i <= s.length; i += 64) {
			md5cycle(state, md5blk(s.substring(i - 64, i)));
		}
		s = s.substring(i - 64);
		var tail = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
		for (i = 0; i < s.length; i++)
		tail[i >> 2] |= s.charCodeAt(i) << ((i % 4) << 3);
		tail[i >> 2] |= 0x80 << ((i % 4) << 3);
		if (i > 55) {
			md5cycle(state, tail);
			for (i = 0; i < 16; i++) tail[i] = 0;
		}
		tail[14] = n * 8;
		md5cycle(state, tail);
		return state;
	}

	function md5blk(s) { /* I figured global was faster.   */
		var md5blks = [], i; /* Andy King said do it this way. */
		for (i = 0; i < 64; i += 4) {
			md5blks[i >> 2] = s.charCodeAt(i) +
			                  (s.charCodeAt(i + 1) << 8) +
			                  (s.charCodeAt(i + 2) << 16) +
			                  (s.charCodeAt(i + 3) << 24);
		}
		return md5blks;
	}

	var hex_chr = '0123456789abcdef'.split('');

	function rhex(n) {
		var s = '', j = 0;
		for (; j < 4; j++)
		s += hex_chr[(n >> (j * 8 + 4)) & 0x0F] +
		     hex_chr[(n >> (j * 8)) & 0x0F];
		return s;
	}

	function hex(x) {
		for (var i = 0; i < x.length; i++)
		x[i] = rhex(x[i]);
		return x.join('');
	}

	md5 = function (s) {
		return hex(md51(s));
	}

	/* this function is much faster, so if possible we use it. Some IEs are the
	only ones I know of that need the idiotic second function, generated by an
	if clause.  */
	function add32(a, b) {
		return (a + b) & 0xFFFFFFFF;
	}

	if (md5('hello') != '5d41402abc4b2a76b9719d911017c592') {
		function add32(x, y) {
			var lsw = (x & 0xFFFF) + (y & 0xFFFF),
			    msw = (x >> 16) + (y >> 16) + (lsw >> 16);
			return (msw << 16) | (lsw & 0xFFFF);
		}
	}
})();

server.R

library(shiny)

shinyServer(function(input, output, clientData) {
  output$testtext <- renderText(paste("     fingerprint: ", input$fingerprint, "     ip: ", input$ipid))
  
  })

shinyBindings.js

  // Calling `jQuery.fingerprint()` will return an MD5 hash, i.e. said
  // fingerprint.

  $.fingerprint = function() {

    // This function, `_raw()`, uses several browser details which are
    // available to JS here to build a string, namely...
    //
    // * the user agent
    // * screen size
    // * color depth
    // * the timezone offset
    // * sessionStorage support
    // * localStorage support
    // * the list of all installed plugins (we're using their names,
    //    descriptions, mime types and file name extensions here)
    function _raw() {
      // That string is the return value.
      return [
        navigator.userAgent,getip(),
        [ screen.height, screen.width, screen.colorDepth ].join("x"),
        ( new Date() ).getTimezoneOffset(),
        !!window.sessionStorage,
        !!window.localStorage,
        $.map( navigator.plugins, function(p) {
          return [
            p.name,
            p.description,
            $.map( p, function(mt) {
              return [ mt.type, mt.suffixes ].join("~");
            }).join(",")
          ].join("::");
        }).join(";")
      ].join("###");
    }

    // `_md5()` computes a MD5 hash using [md5-js](http://github.com/wbond/md5-js/).
    function _md5() {
      if ( typeof window.md5 === "function" ) {
        // The return value is the hashed fingerprint string.
        return md5( _raw() );
      }
      else {
        // If `window.md5()` isn't available, an error is thrown.
        throw "md5 unavailable, please get it from http://github.com/wbond/md5-js/";
      }
    }

    // And, since I'm lazy, calling `$.fingerprint()` will return the hash
    // right away, without the need for any other calls.
    return _md5();
  }

  
  /*
  var outputUserid = new Shiny.OutputBinding();
  $.extend(outputUserid, {
    find: function(scope) {
      return $.find('.userid');
    },
    renderError: function(el,error) {
      console.log("Foe");
    },
    renderValue: function(el,data) {
      updateView(data);
      console.log("Friend");
      
    }
  });
  Shiny.outputBindings.register(outputUserid);
  */
  
  var inputUseridBinding = new Shiny.InputBinding();
  $.extend(inputUseridBinding, {
    find: function(scope) {
      return $.find('.userid');
    },
    getValue: function(el) {
      return $(el).val();
    },
    setValue: function(el, values) {
      $(el).attr("value", $.fingerprint());
      $(el).trigger("change");
    },
    subscribe: function(el, callback) {
      $(el).on("change.inputUseridBinding", function(e) {
        callback();
      });
    },
    unsubscribe: function(el) {
      $(el).off(".inputUseridBinding");
    }
  });
  Shiny.inputBindings.register(inputUseridBinding);
  
  //setuid();

//A unique ID generated from the fingerprint of
// several browser characteristics.
shiny_uid=$.fingerprint();


/*
 * Set the uid fingerprint into the DOM elements that need to know about it.
 * Do not call before the form loads, or the selectors won't find anything.
 */
function setuid() {
  var fph = $('.userid');
  fph.attr("value", shiny_uid);
  fph.trigger("change");
}

function setvalues(){
  getip();
  setuid();
}
/*
 * Set the uid fingerprint into the DOM elements that need to know about it.
 * Do not call before the form loads, or the selectors won't find anything.
 */

var inputIpBinding = new Shiny.InputBinding();
$.extend(inputIpBinding, {
  find: function(scope) {
    return $.find('.ipaddr');
  },
  getValue: function(el) {
    return $(el).val();
  },
  setValue: function(el, values) {
    $(el).attr("value", getip())
    $(el).trigger("change");
  },
  subscribe: function(el, callback) {
    $(el).on("change.inputIpBinding", function(e) {
      callback();
    });
  },
  unsubscribe: function(el) {
    $(el).off(".inputIpBinding");
  }
});
Shiny.inputBindings.register(inputIpBinding);


function getip() {
ip = null;
$.getJSON("http://jsonip.com?callback=?",
  function(data){
       ip = data.ip;
       callback(ip);
       $(".ipaddr").attr("value", ip);
       $(".ipaddr").trigger("change");
 //return ip address correctly
  });
//alert(ip); //undefined or null
}

function callback(tempip)
{
ip=tempip;
// alert(ip); //undefined or null
}

ui.R

library(shiny)

inputUserid <- function(inputId, value='') {
  #   print(paste(inputId, "=", value))
  tagList(
    singleton(tags$head(tags$script(src = "js/md5.js", type='text/javascript'))),
    singleton(tags$head(tags$script(src = "js/shinyBindings.js", type='text/javascript'))),
    tags$body(onload="setvalues()"),
    tags$input(id = inputId, class = "userid", value=as.character(value), type="text", style="display:none;")
  )
}

inputIp <- function(inputId, value=''){
  tagList(
    singleton(tags$head(tags$script(src = "js/md5.js", type='text/javascript'))),
    singleton(tags$head(tags$script(src = "js/shinyBindings.js", type='text/javascript'))),
    tags$body(onload="setvalues()"),
    tags$input(id = inputId, class = "ipaddr", value=as.character(value), type="text", style="display:none;")
  )
}

shinyUI(pageWithSidebar(
  # Application title  
  headerPanel("FingerprintDemo"),
  sidebarPanel(
    inputIp("ipid"),
    inputUserid("fingerprint"),
    helpText("nothing to see here... hidden text elements aren't editable by user")),
  mainPanel(
    textOutput("testtext")
  )
))