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MySQL 5.7 Reference Manual  /  ...  /  Pluggable Authentication

6.3.9 Pluggable Authentication

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 system table. The server then authenticates the client, determining from the account row which authentication plugin applies to the client:

  • If the server cannot find the plugin, an error occurs and the connection attempt is rejected.

  • Otherwise, the server invokes that plugin to authenticate the user, and the plugin returns a status to the server indicating whether the user provided the correct password and is permitted to connect.

Pluggable authentication enables these important capabilities:

  • Choice of authentication methods.  Pluggable authentication makes it easy for DBAs to choose and change the authentication method used for individual MySQL accounts.

  • External authentication.  Pluggable authentication makes it possible for clients to connect to the MySQL server with credentials appropriate for authentication methods that store credentials elsewhere than in the mysql.user system 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 (the proxied user). While the connection lasts, the proxy user is treated, for purposes of access control, as having the privileges of the proxied user. In effect, one user impersonates another. For more information, see Section 6.3.10, “Proxy Users”.

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.

Available Authentication Plugins

MySQL 5.7 provides these authentication plugins:

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 28.2.4.9, “Writing Authentication Plugins”.

Authentication Plugin Usage

This section provides general instructions for installing and using authentication plugins. For instructions specific to a given plugin, see the section that describes that plugin under Section 6.5.1, “Authentication Plugins”.

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

  • If necessary, install the plugin library or libraries containing the appropriate plugins. On the server host, install the library containing the server-side plugin, so that the server can use it to authenticate client connections. Similarly, on each client host, install the library containing the client-side plugin for use by client programs. Authentication plugins that are built in need not be installed.

  • For each MySQL account that you create, specify the appropriate server-side plugin to use for authentication. If the account is to use the default authentication plugin, the account-creation statement need not specify the plugin explicitly. The default_authentication_plugin system variable configures the default authentication plugin.

  • When a client connects, the server-side plugin tells the client program which client-side plugin to use for authentication.

In the case that an account uses an authentication method that is the default for both the server and the client program, the server need not communicate to the client which client-side plugin to use, and a round trip in client/server negotiation can be avoided. This is true for accounts that use native MySQL authentication.

For standard MySQL clients such as mysql and mysqladmin, the --default-auth=plugin_name option can be specified on the command line as a hint about which client-side plugin the program can expect to use, although the server will override this if the server-side plugin associated with the user account requires a different client-side plugin.

If the client program does not find the client-side plugin library file, specify a --plugin-dir=dir_name option to indicate the plugin library directory location.


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