Wiki-to-wiki authentication

Wiki-to-wiki authentication would involve having wikis authenticate themselves to another wiki.

Uses

 * Multi-wiki login, across farms
 * See Eloquence's writings at InstantCommons

Implementation
Here is one three-step possibility:
 * Step 1: Wiki A creates an account on Wiki B
 * Step 2: Wiki A provides Wiki B with a credential, e.g. a password, and an API URL
 * Step 3: Wiki B polls that API URL and receives the password; this verifies the account is indeed operated by Wiki A