In distributed systems, especially in pervasive and ubiquitous environments, mobile users gather certificates providing them rights to access unknown and trusted environments. Such a certificate embeds increasing number of information that leads the certificate provider to adapt existing standards to its requirements. In this paper, we propose a new model of certification called X316 to set up an XML certificates with a contextual morph capability. This morph characteristic enables each certificate owner to disclose and to blind some sensitive certificate parts according to surrounding context. The usability of the X316 is illustrated with the "Chameleon" architecture offering users such a possible access if they appear with trusted certificates. These certificates may be gathered during their roaming in the pervasive environment, and they offer direct or transitive access to foreign sites, based on trust relationships.