The Servlet Specification version 2.4 states in section SRV.15.1.12:
Coherence*Web is fully compliant to the Servlet Specification, and as a result, it does not enable HttpSessionContext by default. However, it does have an option to enable HttpSessionContext, should an application require the ability to enumerate and access HttpSession objects. Using this option, all HttpSession objects across the entire cluster can be enumerated and can be accessed by their session IDs.
To configure the HttpSessionContext to be enabled, edit the coherence-web.xml that is produced from the inspection step of the Coherence*Web Installer. Set the coherence-enable-sessioncontext parameter to true.