public String getGroupAttribute() throws GuacamoleException {
        return environment.getProperty(CASGuacamoleProperties.CAS_GROUP_ATTRIBUTE);
    }
Returns the CAS attribute that should be used to determine group
memberships in CAS, such as "memberOf". If no attribute has been
specified, null is returned.

@return
    The attribute name used to determine group memberships in CAS,
    null if not defined.

@throws GuacamoleException
    If guacamole.properties cannot be parsed.
extensions/guacamole-auth-sso/modules/guacamole-auth-sso-cas/src/main/java/org/apache/guacamole/auth/cas/conf/ConfigurationService.java