1. A method comprising: performing, with a server application in mobile device equipment, bootstrapping procedures between the server application and a bootstrapping server function server; deriving a shared key based on at least a key derived during the bootstrapping procedures; providing a client application with a bootstrapping transaction identifier, wherein the bootstrapping transaction identifier is received from the bootstrapping server function server during the bootstrapping procedures and wherein the client application is capable of communicating with the mobile device equipment; receiving, at the server application, a reply message from the client application; and authenticating, at the server application, the client application by validating the reply message with the shared key, wherein authenticating the client application by validating the reply message with the shared key comprises verifying signed data included in the reply message from the client application, wherein the reply message is generated by the client application in response to receiving a challenge; and wherein the at least the key derived during the bootstrapping procedures is a network application function specific shared secret key.