Testing if URL and querystring is valid
<p>What is the best way to test if a url &amp; querystring is valid? For example, after a login redirect I want to make sure the target url is valid. If not, go to a default page.</p>

<p>We seem to have a problem with the querystring, starting with "ReturnUrl=", being duplicated and that throws an exception. We'd rather have it go to a default page.</p>
