In the Web.config file that is located in the C:\Program Files\Softerra\Adaxes 2\Web Interface folder, specify the users you need in the <authorization> element:
<allow users="email@example.com,firstname.lastname@example.org" />
<deny users="*" />
At the moment it is possible to allow or deny specific users (not groups) to connect to Adaxes Web Interface. In the next version (2011.1) it will be also possible to specify groups.