I have a web app that uses a WCF service that utilizes a behaviorExtension like so:
<behaviorExtensions>
<add name="clientCredentialsExtension" type="
Simon.Web.Giftcard.WCFSecurity.ClientCredentialsExtensionElement,
Simon.Web.Giftcard, Version=1.0.3736.20411, Culture=neutral, PublicKeyToken=null"/>
…