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 traditional 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 external user name passed by the client program, based on the PAM groups the external user is a member of 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, an operating system user named
joe
can connect and have the privileges of a MySQL user nameddeveloper
.
PAM pluggable authentication has been tested on Linux and macOS; note that Windows does not support PAM.
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 6.5 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 mysql_clear_password
cleartext 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 cleartext
plugin in all MySQL distributions enables clients from any
distribution to connect to a server that has the server-side PAM
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 4.17, “Pluggable Authentication”. For information
about the mysql_clear_password
plugin, see
Section 6.1.4, “Client-Side Cleartext Pluggable Authentication”. For proxy
user information, see Section 4.19, “Proxy Users”.
This section provides an overview of how MySQL and PAM work together to authenticate MySQL users. For examples showing how to set up MySQL accounts to use specific PAM services, see Using PAM Pluggable Authentication.
The client program and the server communicate, with the client sending to the server the client user name (the operating system user name by default) and password:
The client user name is the external user name.
For accounts that use the PAM server-side authentication plugin, the corresponding client-side plugin is
mysql_clear_password
. This client-side plugin performs no password hashing, with the result that the client sends the password to the server as cleartext.
The server finds a matching MySQL account based on the external user name and the host from which the client connects. The PAM plugin uses the information passed to it by MySQL Server (such as user name, host name, password, and authentication string). When you define a MySQL account that authenticates using PAM, the authentication string contains:
A PAM service name, which is a name that the system administrator can use to refer to an authentication method for a particular application. There can be multiple applications associated with a single database server instance, so the choice of service name is left to the SQL application developer.
Optionally, if proxying is to be used, a mapping from PAM groups to MySQL user names.
The plugin uses the PAM service named in the authentication string to check the user credentials and returns
'Authentication succeeded, Username is
oruser_name
''Authentication failed'
. The password must be appropriate for the password store used by the PAM service. Examples:For traditional Unix passwords, the service looks up passwords stored in the
/etc/shadow
file.For LDAP, the service looks up passwords stored in an LDAP directory.
If the credentials check fails, the server refuses the connection.
Otherwise, the authentication string indicates whether proxying occurs. If the string contains no PAM group mapping, proxying does not occur. In this case, the MySQL user name is the same as the external user name.
Otherwise, proxying is indicated based on the PAM group mapping, with the MySQL user name determined based on the first matching group in the mapping list. The meaning of “PAM group” depends on the PAM service. Examples:
For traditional Unix passwords, groups are Unix groups defined in the
/etc/group
file, possibly supplemented with additional PAM information in a file such as/etc/security/group.conf
.For LDAP, groups are LDAP groups defined in an LDAP directory.
If the proxy user (the external user) has the
PROXY
privilege for the proxied MySQL user name, proxying occurs, with the proxy user assuming the privileges of the proxied user.
This section describes how to install the server-side PAM authentication plugin. For general information about installing plugins, see 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
, and is typically
compiled with the .so
suffix.
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:
[mysqld]
plugin-load-add=authentication_pam.so
After modifying my.cnf
, restart the
server to cause the new settings to take effect.
Alternatively, to load the plugin at runtime, use this
statement, adjusting 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 without
the need for --plugin-load-add
.
To verify plugin installation, examine the Information Schema
PLUGINS
table or use the
SHOW PLUGINS
statement (see
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.
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 an
INSTALL PLUGIN
statement, it remains installed across server restarts. To uninstall it, useUNINSTALL PLUGIN
:UNINSTALL PLUGIN authentication_pam;
This section describes in general terms how to use the PAM authentication plugin to connect from MySQL client programs to the server. The following sections provide instructions for using PAM authentication in specific ways. It is assumed that the server is running with the server-side PAM 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 'auth_string';
The authentication string specifies the following types of information:
The PAM service name (see How PAM Authentication of MySQL Users Works). Examples in the following discussion use a service name of
mysql-unix
for authentication using traditional Unix passwords, andmysql-ldap
for authentication using LDAP.For proxy support, PAM provides a way for a PAM module to return to the server a MySQL user name other than the external user name passed by the client program when it connects to the server. Use the authentication string to control the mapping from external user names to MySQL user names. If you want to take advantage of proxy user capabilities, the authentication string must include this kind of mapping.
For example, if an account uses the
mysql-unix
PAM service name and should map
operating system users in the root
and
users
PAM groups to the
developer
and data_entry
MySQL users, respectively, use a statement like this:
CREATE USER user
IDENTIFIED WITH authentication_pam
AS 'mysql-unix, 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 PAM group mapping list consisting of one or more keyword/value pairs each specifying a PAM group name and a MySQL user name:
pam_service_name[,pam_group_name=mysql_user_name]...
The plugin parses the authentication string for each connection attempt that uses the account. To minimize overhead, keep the string as short as possible.
Each
pair must be preceded by a comma.pam_group_name
=mysql_user_name
Leading and trailing spaces not inside double quotation marks are ignored.
Unquoted
pam_service_name
,pam_group_name
, andmysql_user_name
values can contain anything except equal sign, comma, or space.If a
pam_service_name
,pam_group_name
, ormysql_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 the external user name (the name passed by the client), it looks for a PAM group mapping list in the authentication string and, if present, uses it to return a different MySQL user name to the MySQL server based on which PAM groups the external user is a member of:
If the authentication string contains no PAM group mapping list, the plugin returns the external name.
If the authentication string does contain a PAM group mapping list, the plugin examines each
pair in the list from left to right and tries to find a match for thepam_group_name
=mysql_user_name
pam_group_name
value in a non-MySQL directory of the groups assigned to the authenticated user and returnsmysql_user_name
for the first match it finds. If the plugin finds no match for any PAM group, it returns the external name. If the plugin is not capable of looking up a group in a directory, it ignores the PAM group mapping list and returns the external 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 PAM authentication. (For a MySQL account of
'
to match the external user,user_name
'@'host_name
'user_name
must be the external user name andhost_name
must match the host from which the client connects.) Authentication can be performed by various PAM-supported methods. Later discussion shows how to authenticate client credentials using traditional Unix passwords, and passwords in LDAP.PAM authentication, when not done through proxy users or PAM groups, requires the MySQL user name to be same as the operating system user name. MySQL user names are limited to 32 characters (see Section 4.3, “Grant Tables”), which limits PAM nonproxy authentication to Unix accounts with names of at most 32 characters.
Proxy users only, with PAM group mapping. For this scenario, create one or more 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 based on the external PAM groups the users are members of) to map all the external user names to the few MySQL accounts holding the privilege sets. Any client who connects and specifies an external user name as the client user name is mapped to one of the MySQL accounts and uses its privileges. The discussion shows how to set this up using traditional Unix passwords, but other PAM methods such as LDAP could be used instead.
Variations on these scenarios are possible:
You can permit some users to log in directly (without proxying) but require others to connect through proxy accounts.
You can use one PAM authentication method for some users, and another method for other users, by using differing PAM service names among your PAM-authenticated accounts. For example, you can use the
mysql-unix
PAM service for some users, andmysql-ldap
for others.
The examples make the following assumptions. You might need to make some adjustments if your system is set up differently.
The login name and password are
antonio
andantonio_password
, respectively. Change these to correspond to the user you want to authenticate.The PAM configuration directory is
/etc/pam.d
.The PAM service name corresponds to the authentication method (
mysql-unix
ormysql-ldap
in this discussion). To use a given PAM service, you must set up a PAM file with the same name in the PAM configuration directory (creating the file if it does not exist). In addition, you must name the PAM service in the authentication string of theCREATE USER
statement for any account that authenticates using that PAM service.
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 issues
that occur when the plugin performs authentication. For more
information, see
PAM Authentication Debugging.
This authentication scenario uses PAM to check external users defined in terms of operating system user names and Unix passwords, without proxying. Every such external user permitted to connect to MySQL Server should have a matching MySQL account that is defined to use PAM authentication through traditional Unix password store.
Traditional Unix passwords are checked using the
/etc/shadow
file. For information
regarding possible issues related to this file, see
PAM Authentication Access to Unix Password Store.
Verify that Unix authentication permits logins to the operating system with the user name
antonio
and passwordantonio_password
.Set up PAM to authenticate MySQL connections using traditional Unix passwords by creating a
mysql-unix
PAM service file named/etc/pam.d/mysql-unix
. 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, themysql-unix
file might look like this:#%PAM-1.0 auth include password-auth account include password-auth
For macOS, use
login
rather thanpassword-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 operating system user name and define it to authenticate using the PAM plugin and the
mysql-unix
PAM service:CREATE USER 'antonio'@'localhost' IDENTIFIED WITH authentication_pam AS 'mysql-unix'; GRANT ALL PRIVILEGES ON mydb.* TO 'antonio'@'localhost';
Here, the authentication string contains only the PAM service name,
mysql-unix
, which authenticates Unix passwords.Use the mysql command-line client to connect to the MySQL server as
antonio
. For example:$> mysql --user=antonio --password --enable-cleartext-plugin Enter password: antonio_password
The server should permit the connection and the following query returns output as shown:
mysql> SELECT USER(), CURRENT_USER(), @@proxy_user; +-------------------+-------------------+--------------+ | USER() | CURRENT_USER() | @@proxy_user | +-------------------+-------------------+--------------+ | antonio@localhost | antonio@localhost | NULL | +-------------------+-------------------+--------------+
This demonstrates that the
antonio
operating system user is authenticated to have the privileges granted to theantonio
MySQL user, and that no proxying has occurred.
The client-side mysql_clear_password
authentication plugin leaves the password untouched, so
client programs send it to the MySQL server as cleartext.
This enables the password to be passed as is to PAM. A
cleartext password 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). See Section 6.1.4, “Client-Side Cleartext Pluggable Authentication”.To avoid password exposure with the
mysql_clear_password
plugin enabled, MySQL clients should connect to the MySQL server using an encrypted connection. See Section 5.1, “Configuring MySQL to Use Encrypted Connections”.
This authentication scenario uses PAM to check external users defined in terms of operating system user names and LDAP passwords, without proxying. Every such external user permitted to connect to MySQL Server should have a matching MySQL account that is defined to use PAM authentication through LDAP.
To use PAM LDAP pluggable authentication for MySQL, these prerequisites must be satisfied:
An LDAP server must be available for the PAM LDAP service to communicate with.
Each LDAP user to be authenticated by MySQL must be present in the directory managed by the LDAP server.
Another way to use LDAP for MySQL user authentication is to use the LDAP-specific authentication plugins. See Section 6.1.7, “LDAP Pluggable Authentication”.
Configure MySQL for PAM LDAP authentication as follows:
Verify that Unix authentication permits logins to the operating system with the user name
antonio
and passwordantonio_password
.Set up PAM to authenticate MySQL connections using LDAP by creating a
mysql-ldap
PAM service file named/etc/pam.d/mysql-ldap
. 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, themysql-ldap
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.
Create a MySQL account with the same user name as the operating system user name and define it to authenticate using the PAM plugin and the
mysql-ldap
PAM service:CREATE USER 'antonio'@'localhost' IDENTIFIED WITH authentication_pam AS 'mysql-ldap'; GRANT ALL PRIVILEGES ON mydb.* TO 'antonio'@'localhost';
Here, the authentication string contains only the PAM service name,
mysql-ldap
, which authenticates using LDAP.Connecting to the server is the same as described in PAM Unix Password Authentication without Proxy Users.
The authentication scheme described here uses proxying and PAM 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 account authenticated using PAM, such that all the external users are mapped to the MySQL accounts that hold the privileges. Any user who connects using the proxy account 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 PAM LDAP Authentication without Proxy Users.
Traditional Unix passwords are checked using the
/etc/shadow
file. For information
regarding possible issues related to this file, see
PAM Authentication Access to Unix Password Store.
Verify that Unix authentication permits logins to the operating system with the user name
antonio
and passwordantonio_password
.Verify that
antonio
is a member of theroot
orusers
PAM group.Set up PAM to authenticate the
mysql-unix
PAM service through operating system users by creating a file named/etc/pam.d/mysql-unix
. 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, themysql-unix
file might look like this:#%PAM-1.0 auth include password-auth account include password-auth
For macOS, use
login
rather thanpassword-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 external PAM users to the proxied accounts:CREATE USER ''@'' IDENTIFIED WITH authentication_pam AS 'mysql-unix, root=developer, users=data_entry';
Here, the authentication string contains the PAM service name,
mysql-unix
, which authenticates Unix passwords. The authentication string also maps external users in theroot
andusers
PAM groups to thedeveloper
anddata_entry
MySQL user names, respectively.The PAM group mapping list following the PAM service name is required when you set up proxy users. Otherwise, the plugin cannot tell how to perform mapping from external user names to the proper proxied MySQL user names.
NoteIf your MySQL installation has anonymous users, they might conflict with the default proxy user. For more information about this issue, and ways of dealing with it, see Default Proxy User and Anonymous User Conflicts.
Create the proxied accounts and grant to each one the privileges it should have:
CREATE USER 'developer'@'localhost' IDENTIFIED WITH mysql_no_login; CREATE USER 'data_entry'@'localhost' IDENTIFIED WITH mysql_no_login; GRANT ALL PRIVILEGES ON mydevdb.* TO 'developer'@'localhost'; GRANT ALL PRIVILEGES ON mydb.* TO 'data_entry'@'localhost';
The proxied accounts use the
mysql_no_login
authentication plugin to prevent clients from using the accounts to log in directly to the MySQL server. Instead, users who authenticate using PAM are expected to use thedeveloper
ordata_entry
account by proxy based on their PAM group. (This assumes that the plugin is installed. For instructions, see Section 6.1.9, “No-Login Pluggable Authentication”.) For alternative methods of protecting proxied accounts against direct use, see Preventing Direct Login to Proxied Accounts.Grant to the proxy account the
PROXY
privilege for each proxied account:GRANT PROXY ON 'developer'@'localhost' TO ''@''; GRANT PROXY ON 'data_entry'@'localhost' TO ''@'';
Use the mysql command-line client to connect to the MySQL server as
antonio
.$> mysql --user=antonio --password --enable-cleartext-plugin Enter password: antonio_password
The server authenticates the connection using the default
''@''
proxy account. The resulting privileges forantonio
depend on which PAM groupsantonio
is a member of. Ifantonio
is a member of theroot
PAM group, the PAM plugin mapsroot
to thedeveloper
MySQL user name and returns that name to the server. The server verifies that''@''
has thePROXY
privilege fordeveloper
and permits the connection. The following query returns output as shown:mysql> SELECT USER(), CURRENT_USER(), @@proxy_user; +-------------------+---------------------+--------------+ | USER() | CURRENT_USER() | @@proxy_user | +-------------------+---------------------+--------------+ | antonio@localhost | developer@localhost | ''@'' | +-------------------+---------------------+--------------+
This demonstrates that the
antonio
operating system user is authenticated to have the privileges granted to thedeveloper
MySQL user, and that proxying occurs through the default proxy account.If
antonio
is not a member of theroot
PAM group but is a member of theusers
PAM group, a similar process occurs, but the plugin mapsuser
PAM group membership to thedata_entry
MySQL user name and returns that name to the server:mysql> SELECT USER(), CURRENT_USER(), @@proxy_user; +-------------------+----------------------+--------------+ | USER() | CURRENT_USER() | @@proxy_user | +-------------------+----------------------+--------------+ | antonio@localhost | data_entry@localhost | ''@'' | +-------------------+----------------------+--------------+
This demonstrates that the
antonio
operating system user is authenticated to have the privileges of thedata_entry
MySQL user, and that proxying occurs through the default proxy account.
The client-side mysql_clear_password
authentication plugin leaves the password untouched, so
client programs send it to the MySQL server as cleartext.
This enables the password to be passed as is to PAM. A
cleartext password 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). See Section 6.1.4, “Client-Side Cleartext Pluggable Authentication”.To avoid password exposure with the
mysql_clear_password
plugin enabled, MySQL clients should connect to the MySQL server using an encrypted connection. See Section 5.1, “Configuring MySQL to Use Encrypted Connections”.
On some systems, Unix authentication uses a password store
such as /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 you are using Unix password store
for PAM authentication, you may be able to enable access to it
from MySQL using one of the following methods:
Assuming that the MySQL server is run from the
mysql
operating system account, put that account in theshadow
group that has/etc/shadow
access:Create a
shadow
group in/etc/group
.Add the
mysql
operating system user to theshadow
group in/etc/group
.Assign
/etc/group
to theshadow
group and enable the group read permission:chgrp shadow /etc/shadow chmod g+r /etc/shadow
Restart the MySQL server.
If you are using the
pam_unix
module and the unix_chkpwd utility, enable password store access as follows:chmod u-s /usr/sbin/unix_chkpwd setcap cap_dac_read_search+ep /usr/sbin/unix_chkpwd
Adjust the path to unix_chkpwd as necessary for your platform.
The PAM authentication plugin checks at initialization time
whether the AUTHENTICATION_PAM_LOG
environment value is set. In MySQL 8.0.35 and earlier, 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 issues that occur when
the plugin performs authentication. You should be aware that,
in these versions, passwords are included in these messages.
Beginning with MySQL 8.0.36, setting
AUTHENTICATION_PAM_LOG=1
(or some other
arbitrary value) produces the same diagnostic messages, but
does not include any passwords. If you
wish to include passwords in these messages, set
AUTHENTICATION_PAM_LOG=PAM_LOG_WITH_SECRET_INFO
.
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.
Another technique for debugging connection failures and determining what is happening during connection attempts is to configure PAM authentication to permit all connections, then check the system log files. This technique should be used only on a temporary basis, and not on a production server.
Configure a PAM service file named
/etc/pam.d/mysql-any-password
with these
contents (the format may differ on some systems):
#%PAM-1.0
auth required pam_permit.so
account required pam_permit.so
Create an account that uses the PAM plugin and names the
mysql-any-password
PAM service:
CREATE USER 'testuser'@'localhost'
IDENTIFIED WITH authentication_pam
AS 'mysql-any-password';
The mysql-any-password
service file causes
any authentication attempt to return true, even for incorrect
passwords. If an authentication attempt fails, that tells you
the configuration problem is on the MySQL side. Otherwise, the
problem is on the operating system/PAM side. To see what might
be happening, check system log files such as
/var/log/secure
,
/var/log/audit.log
,
/var/log/syslog
, or
/var/log/messages
.
After determining what the problem is, remove the
mysql-any-password
PAM service file to
disable any-password access.