6.3.6 Pluggable Authentication

6.3.6 Pluggable Authentication
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When a client connects to the MySQL server, the server uses the user name provided by the client and the client host to select the appropriate account row from the mysql.user table. The server then consults this row to authenticate the client.

Before MySQL 5.5.7, the server authenticates the password provided by the client against the Password column of the account row.

As of MySQL 5.5.7, the server authenticates clients using a plugin. Selection of the proper account row from the mysql.user table is based on the user name and client host, as before, but the server authenticates the client by determining from the account row which authentication plugin applies for the client:

If the account row specifies a plugin, the server invokes it to authenticate the user. If the server cannot find the plugin, an error occurs.
If the account row specifies no plugin name, the server authenticates the account using either the mysql_native_password or mysql_old_password plugin, depending on whether the password hash value in the Password column used native hashing or the older pre-4.1 hashing method. Clients must match the password in the Password column of the account row.

The plugin returns a status to the server indicating whether the user is permitted to connect.

Pluggable authentication enables two important capabilities:

External authentication: Pluggable authentication makes it possible for clients to connect to the MySQL server with credentials that are appropriate for authentication methods other than native authentication based on passwords stored in the mysql.user table. For example, plugins can be created to use external authentication methods such as PAM, Windows login IDs, LDAP, or Kerberos.
Proxy users: If a user is permitted to connect, an authentication plugin can return to the server a user name different from the name of the connecting user, to indicate that the connecting user is a proxy for another user. While the connection lasts, the proxy user is treated, for purposes of access control, as having the privileges of a different user. In effect, one user impersonates another. For more information, see Section 6.3.7, “Proxy Users”.

Several authentication plugins are available in MySQL:

Plugins that perform native authentication that matches the password against the Password column of the account row. The mysql_native_password plugin implements authentication based on the native password hashing method. The mysql_old_password plugin implements native authentication based on the older (pre-4.1) password hashing method. See Section 6.5.1.1, “The Native Authentication Plugin”, and Section 6.5.1.2, “The Old Native Authentication Plugin”. Native authentication using mysql_native_password is the default for accounts that have no plugin named explicitly in their account row.
A plugin that performs external authentication against PAM (Pluggable Authentication Modules), enabling MySQL Server to use PAM to authenticate MySQL users. This plugin supports proxy users as well. See Section 6.5.1.3, “The PAM Authentication Plugin”.
A plugin that performs external authentication on Windows, enabling MySQL Server to use native Windows services to authenticate client connections. Users who have logged in to Windows can connect from MySQL client programs to the server based on the information in their environment without specifying an additional password. This plugin supports proxy users as well. See Section 6.5.1.4, “The Windows Native Authentication Plugin”.
A client-side plugin that sends the password to the server without hashing or encryption. This plugin can be used by server-side plugins that require access to the password exactly as provided by the client user. See Section 6.5.1.5, “The Cleartext Client-Side Authentication Plugin”.
A plugin that authenticates clients that connect from the local host through the Unix socket file. See Section 6.5.1.6, “The Socket Peer-Credential Authentication Plugin”.
A test plugin that authenticates using MySQL native authentication. This plugin is intended for testing and development purposes, and as an example of how to write an authentication plugin. See Section 6.5.1.7, “The Test Authentication Plugin”.

Note

For information about current restrictions on the use of pluggable authentication, including which connectors support which plugins, see Section C.9, “Restrictions on Pluggable Authentication”.

Third-party connector developers should read that section to determine the extent to which a connector can take advantage of pluggable authentication capabilities and what steps to take to become more compliant.

If you are interested in writing your own authentication plugins, see Section 24.2.4.9, “Writing Authentication Plugins”.

Authentication Plugin Usage Instructions

This section provides general instructions for installing and using authentication plugins.

In general, pluggable authentication uses corresponding plugins on the server and client sides, so you use a given authentication method like this:

On the server host, install the library containing the appropriate server plugin, if necessary, so that the server can use it to authenticate client connections. Similarly, on each client host, install the library containing the appropriate client plugin for use by client programs.
Create MySQL accounts that specify use of the plugin for authentication.
When a client connects, the server plugin tells the client program which client plugin to use for authentication.

The instructions here use an example authentication plugin included in MySQL distributions (see Section 6.5.1.7, “The Test Authentication Plugin”). The procedure is similar for other authentication plugins; substitute the appropriate plugin and file names.

The example authentication plugin has these characteristics:

The server-side plugin name is test_plugin_server.
The client-side plugin name is auth_test_plugin.
Both plugins are located in the shared library file named auth_test_plugin.so in the plugin directory (the directory named by the plugin_dir system variable). The file name suffix might differ on your system.

Install and use the example authentication plugin as follows:

Make sure that the plugin library is installed on the server and client hosts.
Install the server-side test plugin at server startup or at runtime:
- To install the plugin at startup, use the --plugin-load option. With this plugin-loading method, the option must be given each time you start the server. For example, use these lines in a my.cnf option file:
```
[mysqld]
plugin-load=test_plugin_server=auth_test_plugin.so
```
- To install the plugin at runtime, use the INSTALL PLUGIN statement:
```
INSTALL PLUGIN test_plugin_server SONAME 'auth_test_plugin.so';
```
  This installs the plugin permanently and need be done only once.

Verify that the plugin is installed. For example, use SHOW PLUGINS:

mysql> SHOW PLUGINS\G
...
*************************** 21. row ***************************
   Name: test_plugin_server
 Status: ACTIVE
   Type: AUTHENTICATION
Library: auth_test_plugin.so
License: GPL

For other ways to check the plugin, see Section 5.5.3, “Obtaining Server Plugin Information”.

To specify that a MySQL user must be authenticated using a specific server plugin, name the plugin in the IDENTIFIED WITH clause of the CREATE USER statement that creates the user:
```
CREATE USER 'testuser'@'localhost' IDENTIFIED WITH test_plugin_server;
```
Connect to the server using a client program. The test plugin authenticates the same way as native MySQL authentication, so provide the usual --user and --password options that you normally use to connect to the server. For example:
```
shell> mysql --user=your_name --password=your_pass
```
For connections by testuser, the server sees that the account must be authenticated using the server-side plugin named test_plugin_server and communicates to the client program which client-side plugin it must use—in this case, auth_test_plugin.
In the case that the account uses the authentication method that is the default for both the server and the client program, the server need not communicate to the client which plugin to use, and a round trip in client/server negotiation can be avoided. This is true for accounts that use native MySQL authentication (mysql_native_password).
The --default-auth=plugin_name option can be specified on the mysql command line as a hint about which client-side plugin the program can expect to use, although the server will override this if the user account requires a different plugin.
If the client program does not find the plugin, specify a --plugin-dir=dir_name option to indicate where the plugin is located.

Note

If you start the server with the --skip-grant-tables option, authentication plugins are not used even if loaded because the server performs no client authentication and permits any client to connect. Because this is insecure, you might want to use --skip-grant-tables in conjunction with --skip-networking to prevent remote clients from connecting.

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