Review of Projects/Kadmin hook interface

[Sam Hartman]

I've started a review of
http://k5wiki.kerberos.org/wiki/Projects/Kadmin_hook_interface; send
comments by 2010-10-06.

Here is the brief overview; see the wiki for a proposed header file.
   The Kadm5 hook interface provides a plugin interface for plugins to be
   aware of administrative operations for kadm5 principals. Plugins track
   the following administrative operations:
     * Principal creation
     * Change password
     * Principal modification

   The plugins are called twice: once in a precommit phase before the
   operation takes place and if no plugins fail and the database is
   updated, once in a postcommit operation. This interface is based on a
   proposed patch to Heimdal by Russ Allbery for the [8]krb5-sync plugin.
   Russ indicated that Heimdal is likely to adopt an approach based on
   stackable database plugins rather than his approach. That's probably
   undesirable for MIT because the kadm5 API is more stable than the KDB
   API and because this interface is easier for plugin authors than
   writing a KDB module. This interface has the following changes from
   Russ's interface:
    1. Opaque struct rather than void * for the module context
    2. Include key-salt tuples for create/chpass
    3. Add a remove entry point
    4. Remove name and vendor entries to be consistent with other plugin
       framework uses