Well you can use JQuery and attach an attribute to be selected for the passwords to validate each other via input
event. Use setCustomValidity() to set the message of the input affected to override the default message when the form is submitted.
See the updated fiddle.
As you can see in the fiddle, all you have to do is add an attribute data-equal-id
wherein the attribute value must be the ID of password input element to be tested.
HTML
<h1>How to create html5 validation for password confirm?</h1>
<hr>
<form>
<label>Login:</label>
<input type="text" name="login" id="login"/><br/>
<label>Password:</label>
<input type="password" name="pass" id="pass"/><br/>
<label>Password Confirm:</label>
<input type="password" name="pass_conf" id="pass_conf" data-equal-id="pass" /><br/>
<input type="submit"/>
</form>
Javascript
$('[data-equal-id]').bind('input', function() {
var to_confirm = $(this);
var to_equal = $('#' + to_confirm.data('equalId'));
if(to_confirm.val() != to_equal.val())
this.setCustomValidity('Password must be equal');
else
this.setCustomValidity('');
});