A system and method for user certificate initiation, distribution, and provisioning in converged WLAN-WWAN interworking networks. A computing device operable in a wireless local area network sends a public key to a mobile device operable in a wireless cellular wide area network. The mobile device performs a bootstrapping procedure with a cellular operator in the wireless cellular wide area network to obtain a user certificate based on the public key. The mobile device sends the user certificate to the computing device for installation on the computing device. The user certificate may be used for digital signature, verification, and encryption purposes. The user certificate is also used in both the wireless local area network and the wireless wide area network for authenticating a subscriber when accessing services from both networks.