The svn_auth_cleanup_walk() API was introduced on trunk as a way to give
programmatically access to the process of selectively deleting authentication
credentials cached by Subversion. The concept makes sense well enough -- call a
function which drives a callback which answers to "to delete or not to delete"
question. But the implementation, unfortunately, leaves much to be desired.
In r1465119 (http://svn.apache.org/r1465119), I dropped some "### FIXME"
comments into the codebase to point out some of my larger concerns with this
code, and hope to resolve them next week.