Unpredictable Unique Identifier
<p>For an application I am working on, I need to generate a session token which must have following properties:</p>

<ul>
<li>it should be unique for the application at least, globally unique would be even better</li>
<li>it should be unpredictable</li>
<li>it should not be too long, as it will have to be passed around in a http request header, so smaller is better</li>
</ul>

<p>I was thinking about adapting a Guid structure with a cryptographic random number, but it may be an overkill. Anyone know/created a data structure that would fit all those properties?</p>
