Wiki aims to be welcoming. The user experience greets the user from the first page, with an invite to write. This very act is an invitation to engage in insecure behaviour. The idea that you can write on a site without appropriate credentials is a a transgression of best security practice. Wiki and security are uncomfortable bed fellows.
A public key infrastructure (PKI) is a set of roles, policies, and procedures needed to create, manage, distribute, use, store, and revoke digital certificates and manage public-key encryption - wikipedia 