Support SET PASSWORD for authentication plugins.
Authentication plugin API is extended with two optional methods:
* hash_password() is used to compute a password hash (or digest)
from the plain-text password. This digest will be stored in mysql.user
table
* preprocess_hash() is used to convert this digest into some memory
representation that can be later used to authenticate a user.
Build-in plugins convert the hash from hexadecimal or base64 to binary,
to avoid doing it on every authentication attempt.
Note a change in behavior: when loading privileges (on startup or on
FLUSH PRIVILEGES) an account with an unknown plugin was loaded with a
warning (e.g. "Plugin 'foo' is not loaded"). But such an account could
not be used for authentication until the plugin is installed. Now an
account like that will not be loaded at all (with a warning, still).
Indeed, without plugin's preprocess_hash() method the server cannot know
how to load an account. Thus, if a new authentication plugin is
installed run-time, one might need FLUSH PRIVILEGES to activate all
existing accounts that were using this new plugin.
Remove ONLY_IF clause in MYSQL_ADD_PLUGIN and the requirement
that every plugin's CMakeLists.txt *must* do MYSQL_ADD_PLUGIN
for PLUGIN_XXX=YES to work. This was very fragile and cannot be
relied on.
Use a different implementation of =YES check - iterate all
PLUGIN_* variables and see which one doesn't have a matching target.
Revert all ONLY_IF changes in CMakeLists.txt files.
* Introduce a set of PLUGIN_xxx cmake options with values
NO, STATIC, DYNAMIC, AUTO, YES (abort if plugin is not compiled)
* Deprecate redundant and ambiguous WITH_xxx, WITH_PLUGIN_xxx,
WITH_xxx_STORAGE_ENGINE, WITHOUT_xxx, WITHOUT_PLUGIN_xxx,
WITHOUT_xxx_STORAGE_ENGINE
* Actually check whether a plugin is disabled (DISABLED keyword was
always present, but it was ignored until now).
* Support conditionally disabled plugins - keyword ONLY_IF
* Use ONLY_IF for conditionally skipping plugins, instead of
doing MYSQL_ADD_PLUGIN conditionally as before. Because if
MYSQL_ADD_PLUGIN isn't done at all, PLUGIN_xxx=YES cannot work.
out of libmysql into separate dynamic plugins in the plugin/ directory.
move dialog and auth_socket plugins out of the plugin directory with examples into
dedicated directories in plugin/
