introduce the syntax
... IDENTIFIED { WITH | VIA }
plugin [ { USING | AS } auth ]
[ OR plugin [ { USING | AS } auth ]
[ OR ... ]]
Server will try auth plugins in the specified order until the first
success. No protocol changes, server uses the existing "switch plugin"
packet.
The auth chain is stored in json as
"auth_or":[{"plugin":"xxx","authentication_string":"yyy"},
{},
{"plugin":"foo","authentication_string":"bar"},
...],
"plugin":"aaa", "authentication_string":"bbb"
Note:
* "auth_or" implies that there might be "auth_and" someday;
* one entry in the array is an empty object, meaning to take plugin/auth
from the main json object. This preserves compatibility with
the existing mysql.global_priv table and with the mysql.user view.
This entry is preferrably a mysql_native_password plugin for a
non-empty mysql.user.password column.
SET PASSWORD is supported and changes the password for the *first*
plugin in the chain that has a notion of a "password"
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.
Don't distinguish between a "password hash" and "authentication string"
anymore. Now both are stored in mysql.user.authentication_string, both
are handled identically internally. A "password hash" is just how some
particular plugins interpret authentication string.
Set mysql.user.plugin even if there is no password. The server will use
mysql_native_password plugin in these cases, let's make it expicit.
Remove LEX_USER::pwhash.
