This article applies to the following:
A BlackBerry® Enterprise Server administrator may wish to restrict push access on the BlackBerry MDS Connection Service. If this has been enabled, a push application must provide an appropriate username and password, or else the push request will not be accepted and the push application would receive a 403 Access Denied error.
If push access control is enabled, a push request should provide an appropriate username and password using Hypertext Transfer Protocol (HTTP) Basic authentication.
Article this article has further information on implementing HTTP Basic authentication in a BlackBerry device application.