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6.5.1.5 PAM Pluggable Authentication

Table des matières

Note

PAM pluggable authentication is an extension included in MySQL Enterprise Edition, a commercial product. To learn more about commercial products, see https://www.mysql.com/products/.

MySQL Enterprise Edition supports an authentication method that enables MySQL Server to use PAM (Pluggable Authentication Modules) to authenticate MySQL users. PAM enables a system to use a standard interface to access various kinds of authentication methods, such as Unix passwords or an LDAP directory.

PAM pluggable authentication provides these capabilities:

External authentication: PAM authentication enables MySQL Server to accept connections from users defined outside the MySQL grant tables and that authenticate using methods supported by PAM.
Proxy user support: PAM authentication can return to MySQL a user name different from the login user, based on the groups the external user is in and the authentication string provided. This means that the plugin can return the MySQL user that defines the privileges the external PAM-authenticated user should have. For example, a user named joe can connect and have the privileges of the user named developer.

PAM pluggable authentication has been tested on Linux and macOS.

The PAM plugin uses the information passed to it by MySQL Server (such as user name, host name, password, and authentication string), plus whatever method is available for PAM lookup. The plugin checks the user credentials against PAM and returns 'Authentication succeeded, Username is user_name' or 'Authentication failed'.

The following table shows the plugin and library file names. The file name suffix might differ on your system. The file must be located in the directory named by the plugin_dir system variable. For installation information, see Installing PAM Pluggable Authentication.

Table 6.17 Plugin and Library Names for PAM Authentication

Plugin or File	Plugin or File Name
Server-side plugin	`authentication_pam`
Client-side plugin	`mysql_clear_password`
Library file	`authentication_pam.so`

The client-side clear-text plugin that communicates with the server-side PAM plugin is built into the libmysqlclient client library and is included in all distributions, including community distributions. Inclusion of the client-side clear-text plugin in all MySQL distributions enables clients from any distribution to connect to a server that has the server-side plugin loaded.

The following sections provide installation and usage information specific to PAM pluggable authentication:

For general information about pluggable authentication in MySQL, see Section 6.3.10, “Pluggable Authentication”. For information about the mysql_clear_password plugin, see Section 6.5.1.4, “Client-Side Cleartext Pluggable Authentication”. For proxy user information, see Section 6.3.11, “Proxy Users”.

Installing PAM Pluggable Authentication

This section describes how to install the PAM authentication plugin. For general information about installing plugins, see Section 5.6.1, “Installing and Uninstalling Plugins”.

To be usable by the server, the plugin library file must be located in the MySQL plugin directory (the directory named by the plugin_dir system variable). If necessary, configure the plugin directory location by setting the value of plugin_dir at server startup.

The plugin library file base name is authentication_pam. The file name suffix differs per platform (for example, .so for Unix and Unix-like systems, .dll for Windows).

To load the plugin at server startup, use the --plugin-load-add option to name the library file that contains it. With this plugin-loading method, the option must be given each time the server starts. For example, put these lines in the server my.cnf file (adjust the .so suffix for your platform as necessary):

[mysqld]
plugin-load-add=authentication_pam.so

After modifying my.cnf, restart the server to cause the new settings to take effect.

Alternatively, to register the plugin at runtime, use this statement (adjust the .so suffix as necessary):

INSTALL PLUGIN authentication_pam SONAME 'authentication_pam.so';

INSTALL PLUGIN loads the plugin immediately, and also registers it in the mysql.plugins system table to cause the server to load it for each subsequent normal startup.

To verify plugin installation, examine the INFORMATION_SCHEMA.PLUGINS table or use the SHOW PLUGINS statement (see Section 5.6.2, “Obtaining Server Plugin Information”). For example:

mysql> SELECT PLUGIN_NAME, PLUGIN_STATUS
FROM INFORMATION_SCHEMA.PLUGINS
WHERE PLUGIN_NAME LIKE '%pam%';
+--------------------+---------------+
| PLUGIN_NAME | PLUGIN_STATUS |
+--------------------+---------------+
| authentication_pam | ACTIVE |
+--------------------+---------------+

If the plugin fails to initialize, check the server error log for diagnostic messages.

To associate MySQL accounts with the PAM plugin, see Using PAM Pluggable Authentication.

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Uninstalling PAM Pluggable Authentication

The method used to uninstall the PAM authentication plugin depends on how you installed it:

If you installed the plugin at server startup using a --plugin-load-add option, restart the server without the option.
If you installed the plugin at runtime using INSTALL PLUGIN, it remains installed across server restarts. To uninstall it, use UNINSTALL PLUGIN:
1. UNINSTALL PLUGIN authentication_pam;

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Using PAM Pluggable Authentication

This section describes how to use the PAM authentication plugin to connect from MySQL client programs to the server. It is assumed that the server is running with the server-side plugin enabled, as described in Installing PAM Pluggable Authentication.

To refer to the PAM authentication plugin in the IDENTIFIED WITH clause of a CREATE USER statement, use the name authentication_pam. For example:

CREATE USER user
IDENTIFIED WITH authentication_pam
AS 'authentication_string';

The authentication string specifies the following types of information:

PAM supports the notion of “service name,” which is a name that the system administrator can use to configure the authentication method for a particular application. There can be several such “applications” associated with a single database server instance, so the choice of service name is left to the SQL application developer. When you define an account that should authenticate using PAM, specify the service name in the authentication string.
PAM provides a way for a PAM module to return to the server a MySQL user name other than the login name supplied at login time. Use the authentication string to control the mapping between login name and MySQL user name. If you want to take advantage of proxy user capabilities, the authentication string must include this kind of mapping.

For example, if the service name is mysql and users in the root and users PAM groups should be mapped to the developer and data_entry MySQL users, respectively, use a statement like this:

CREATE USER user
IDENTIFIED WITH authentication_pam
AS 'mysql, root=developer, users=data_entry';

Authentication string syntax for the PAM authentication plugin follows these rules:

The string consists of a PAM service name, optionally followed by a group mapping list consisting of one or more keyword/value pairs each specifying a group name and a MySQL user name:
```
pam_service_name[,group_name=mysql_user_name]...
```
The plugin parses the authentication string on each login check. To minimize overhead, keep the string as short as possible.
Each group_name=mysql_user_name pair must be preceded by a comma.
Leading and trailing spaces not inside double quotation marks are ignored.
Unquoted pam_service_name, group_name, and mysql_user_name values can contain anything except equal sign, comma, or space.
If a pam_service_name, group_name, or mysql_user_name value is quoted with double quotation marks, everything between the quotation marks is part of the value. This is necessary, for example, if the value contains space characters. All characters are legal except double quotation mark and backslash (\). To include either character, escape it with a backslash.

If the plugin successfully authenticates a login name, it looks for a group mapping list in the authentication string and, if present, uses it to return a different user name to the MySQL server based on the groups the external user is a member of:

If the authentication string contains no group mapping list, the plugin returns the login name.
If the authentication string does contain a group mapping list, the plugin examines each group_name=mysql_user_name pair in the list from left to right and tries to find a match for the group_name value in a non-MySQL directory of the groups assigned to the authenticated user and returns mysql_user_name for the first match it finds. If the plugin finds no match for any group, it returns the login name. If the plugin is not capable of looking up a group in a directory, it ignores the group mapping list and returns the login name.

The following sections describe how to set up several authentication scenarios that use the PAM authentication plugin:

No proxy users. This uses PAM only to check login names and passwords. Every external user permitted to connect to MySQL Server should have a matching MySQL account that is defined to use external PAM authentication. (For a MySQL account of user_name@host_name to match the external user, user_name must be the login name and host_name must match the host from which the client connects.) Authentication can be performed by various PAM-supported methods. The discussion shows how to use traditional Unix passwords and LDAP.
PAM authentication, when not done through proxy users or groups, requires the MySQL account to have the same user name as the Unix account. MySQL user names are limited to 32 characters (see Section 6.2.3, “Grant Tables”), which limits PAM nonproxy authentication to Unix accounts with names of at most 32 characters.
Proxy login only and group mapping. For this scenario, create one or a few MySQL accounts that define different sets of privileges. (Ideally, nobody should connect using those accounts directly.) Then define a default user authenticating through PAM that uses some mapping scheme (usually by the external groups the users are in) to map all the external logins to the few MySQL accounts holding the privilege sets. Any user that logs in is mapped to one of the MySQL accounts and uses its privileges. The discussion shows how to set this up using Unix passwords, but other PAM methods such as LDAP could be used instead.

Variations on these scenarios are possible. For example, you can permit some users to log in directly (without proxying) but require others to connect through proxy users.

The examples make the following assumptions. You might need to make some adjustments if your system is set up differently.

The PAM configuration directory is /etc/pam.d.
The PAM service name is mysql, which means that you must set up a PAM file named mysql in the PAM configuration directory (creating the file if it does not exist). If you use a service name different from mysql, the file name will differ and you must use a different name in the AS 'auth_string' clause of CREATE USER statements.
The examples use a login name of antonio and password of verysecret. Change these to correspond to the users you want to authenticate.

The PAM authentication plugin checks at initialization time whether the AUTHENTICATION_PAM_LOG environment value is set in the server's startup environment. If so, the plugin enables logging of diagnostic messages to the standard output. Depending on how your server is started, the message might appear on the console or in the error log. These messages can be helpful for debugging PAM-related problems that occur when the plugin performs authentication. For more information, see PAM Pluggable Authentication Debugging.

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Unix Password Authentication without Proxy Users

This authentication scenario uses PAM only to check Unix user login names and passwords. Every external user permitted to connect to MySQL Server should have a matching MySQL account that is defined to use external PAM authentication.

Verify that Unix authentication in PAM permits you to log in as antonio with password verysecret.
Set up PAM to authenticate the mysql service by creating a file named /etc/pam.d/mysql. The file contents are system dependent, so check existing login-related files in the /etc/pam.d directory to see what they look like. On Linux, the mysql file might look like this:
```
#%PAM-1.0
auth            include         password-auth
account         include         password-auth
```
For Gentoo Linux, use system-login rather than password-auth. For macOS, use login rather than password-auth.
The PAM file format might differ on some systems. For example, on Ubuntu and other Debian-based systems, use these file contents instead:
```
@include common-auth
@include common-account
@include common-session-noninteractive
```
Create a MySQL account with the same user name as the Unix login name and define it to authenticate using the PAM plugin:
1. CREATE USER 'antonio'@'localhost'
2. IDENTIFIED WITH authentication_pam AS 'mysql';
3. GRANT ALL PRIVILEGES ON mydb.* TO 'antonio'@'localhost';
Connect to the MySQL server using the mysql command-line client. For example:
```
mysql --user=antonio --password --enable-cleartext-plugin mydb
Enter password: verysecret
```
The server should permit the connection and the following query should return output as shown:
1. mysql> SELECT USER(), CURRENT_USER(), @@proxy_user;
2. +-------------------+-------------------+--------------+
3. | USER() | CURRENT_USER() | @@proxy_user |
4. +-------------------+-------------------+--------------+
5. | antonio@localhost | antonio@localhost | NULL |
6. +-------------------+-------------------+--------------+
This demonstrates that antonio uses the privileges granted to the antonio MySQL account, and that no proxying has occurred.

Note

The client-side mysql_clear_password plugin with which the server-side PAM plugin communicates sends the password to the MySQL server in clear text so it can be passed to PAM. This is necessary to use the server-side PAM library, but may be a security problem in some configurations. These measures minimize the risk:

To make inadvertent use of the mysql_clear_password plugin less likely, MySQL clients must explicitly enable it; for example, with the --enable-cleartext-plugin option.
To avoid password exposure with the mysql_clear_password plugin enabled, MySQL clients should connect to the MySQL server using a secure connection.

For additinal information, see Section 6.5.1.4, “Client-Side Cleartext Pluggable Authentication”, and Section 6.4.1, “Configuring MySQL to Use Encrypted Connections”.

Note

On some systems, Unix authentication uses /etc/shadow, a file that typically has restricted access permissions. This can cause MySQL PAM-based authentication to fail. Unfortunately, the PAM implementation does not permit distinguishing “password could not be checked” (due, for example, to inability to read /etc/shadow) from “password does not match.” If your system uses /etc/shadow, you may be able enable access to it by MySQL using this method (assuming that the MySQL server is run from the mysql system account):

Create a shadow group in /etc/group.
Add the mysql user to the shadow group in /etc/group.
Assign /etc/group to the shadow group and enable the group read permission:
```
chgrp shadow /etc/shadow
chmod g+r /etc/shadow
```
Restart the MySQL server.

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LDAP Authentication without Proxy Users

This authentication scenario uses PAM only to check LDAP user login names and passwords. Every external user permitted to connect to MySQL Server should have a matching MySQL account that is defined to use external PAM authentication.

Verify that LDAP authentication in PAM permits you to log in as antonio with password verysecret.
Set up PAM to authenticate the mysql service through LDAP by creating a file named /etc/pam.d/mysql. The file contents are system dependent, so check existing login-related files in the /etc/pam.d directory to see what they look like. On Linux, the mysql file might look like this:
```
#%PAM-1.0
auth        required    pam_ldap.so
account     required    pam_ldap.so
```
If PAM object files have a suffix different from .so on your system, substitute the correct suffix.
The PAM file format might differ on some systems.
MySQL account creation and connecting to the server is the same as described in Unix Password Authentication without Proxy Users.

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Unix Password Authentication with Proxy Users and Group Mapping

The authentication scheme described here uses proxying and group mapping to map connecting MySQL users who authenticate using PAM onto other MySQL accounts that define different sets of privileges. Users do not connect directly through the accounts that define the privileges. Instead, they connect through a default proxy user authenticated using PAM, such that all the external logins are mapped to the MySQL accounts that hold the privileges. Any user who connects is mapped to one of those MySQL accounts, the privileges for which determine the database operations permitted to the external user.

The procedure shown here uses Unix password authentication. To use LDAP instead, see the early steps of LDAP Authentication without Proxy Users.

Note

For information regarding possible problems related to /etc/shadow, see Unix Password Authentication without Proxy Users.

Verify that Unix authentication in PAM permits you to log in as antonio with password verysecret and that antonio is a member of the root or users group.
Set up PAM to authenticate the mysql service. Put the following in /etc/pam.d/mysql:
```
#%PAM-1.0
auth            include         password-auth
account         include         password-auth
```
For Gentoo Linux, use system-login rather than password-auth. For macOS, use login rather than password-auth.
The PAM file format might differ on some systems. For example, on Ubuntu and other Debian-based systems, use these file contents instead:
```
@include common-auth
@include common-account
@include common-session-noninteractive
```
Create a default proxy user (''@'') that maps the external PAM users to the proxied accounts. It maps external users from the root PAM group to the developer MySQL account and the external users from the users PAM group to the data_entry MySQL account:
1. CREATE USER ''@''
2. IDENTIFIED WITH authentication_pam
3. AS 'mysql, root=developer, users=data_entry';
The mapping list following the service name is required when you set up proxy users. Otherwise, the plugin cannot tell how to map the name of PAM groups to the proper proxied user name.

Note

If your MySQL installation has anonymous users, they might conflict with the default proxy user. For more information about this problem, and ways of dealing with it, see Default Proxy User and Anonymous User Conflicts.
Create the proxied accounts that will be used to access the databases:
1. CREATE USER 'developer'@'localhost' IDENTIFIED BY 'very secret password';
2. GRANT ALL PRIVILEGES ON mydevdb.* TO 'developer'@'localhost';
3. CREATE USER 'data_entry'@'localhost' IDENTIFIED BY 'very secret password';
4. GRANT ALL PRIVILEGES ON mydb.* TO 'data_entry'@'localhost';
If you do not let anyone know the passwords for these accounts, other users cannot use them to connect directly to the MySQL server. Instead, it is expected that users will authenticate using PAM and that they will use the developer or data_entry account by proxy based on their PAM group.
Grant the PROXY privilege to the proxy account for each proxied account:
1. GRANT PROXY ON 'developer'@'localhost' TO ''@'';
2. GRANT PROXY ON 'data_entry'@'localhost' TO ''@'';
Connect to the MySQL server using the mysql command-line client. For example:
```
mysql --user=antonio --password --enable-cleartext-plugin mydb
Enter password: verysecret
```
The server authenticates the connection using the ''@'' account. The privileges antonio will have depends on what PAM groups he is a member of. If antonio is a member of the root PAM group, the PAM plugin maps root to the developer MySQL user name and returns that name to the server. The server verifies that ''@'' has the PROXY privilege for developer and permits the connection. the following query should return output as shown:
1. mysql> SELECT USER(), CURRENT_USER(), @@proxy_user;
2. +-------------------+---------------------+--------------+
3. | USER() | CURRENT_USER() | @@proxy_user |
4. +-------------------+---------------------+--------------+
5. | antonio@localhost | developer@localhost | ''@'' |
6. +-------------------+---------------------+--------------+
This demonstrates that antonio uses the privileges granted to the developer MySQL account, and that proxying occurred through the default proxy user account.
If antonio is not a member of the root PAM group but is a member of the users group, a similar process occurs, but the plugin maps user group membership to the data_entry MySQL user name and returns that name to the server. In this case, antonio uses the privileges of the data_entry MySQL account:
1. mysql> SELECT USER(), CURRENT_USER(), @@proxy_user;
2. +-------------------+----------------------+--------------+
3. | USER() | CURRENT_USER() | @@proxy_user |
4. +-------------------+----------------------+--------------+
5. | antonio@localhost | data_entry@localhost | ''@'' |
6. +-------------------+----------------------+--------------+

Note

To make inadvertent use of the mysql_clear_password plugin less likely, MySQL clients must explicitly enable it; for example, with the --enable-cleartext-plugin option.
To avoid password exposure with the mysql_clear_password plugin enabled, MySQL clients should connect to the MySQL server using a secure connection.

For additinal information, see Section 6.5.1.4, “Client-Side Cleartext Pluggable Authentication”, and Section 6.4.1, “Configuring MySQL to Use Encrypted Connections”.

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PAM Pluggable Authentication Debugging

The PAM authentication plugin checks at initialization time whether the AUTHENTICATION_PAM_LOG environment value is set (the value does not matter). If so, the plugin enables logging of diagnostic messages to the standard output. These messages may be helpful for debugging PAM-related problems that occur when the plugin performs authentication.

Some messages include reference to PAM plugin source files and line numbers, which enables plugin actions to be tied more closely to the location in the code where they occur.

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Document créé le 26/06/2006, dernière modification le 26/10/2018
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