LDAP with auth_pam and Python to authenticate against MySQL

If that title looks familiar, it is because a few months ago I posted about LDAP with auth_pam and PHP to authenticate against MySQL.

The good news is that recompiling the connector for Python is a lot easier than for PHP. With PHP, the complexity was due to there being one monolithic package to recompile. The bad news is that there is a slight hitch with Python.

Skip down to the hitch and how to compile MySQLdb for use with auth_pam plugin.

As a quick reminder, here is a repeat of the background:

Background


There are two plugins that can be used. From the documentation, the two plugins are:

  • Full PAM plugin called auth_pam. This plugin uses dialog.so. It fully supports the PAM protocol with arbitrary communication between client and server.
  • Oracle-compatible PAM called auth_pam_compat. This plugin uses mysql_clear_password which is a part of Oracle MySQL client. It also has some limitations, such as, it supports only one password input. You must use -p option in order to pass the password to auth_pam_compat.

Percona’s MySQL client supports both plugins natively. That is, you can use auth_pam or auth_pam_compat and use the “mysql” tool (or “mysqldump”, or mysql_upgrade, etc.) and you are good to go. Given the choice, we would all use auth_pam, under which clients DO NOT use mysql_clear_password.

Not all clients support auth_pam, which is the main problem. Workarounds have called for using auth_pam_compat over SSL, which is a perfectly reasonable way to handle the risk of cleartext passwords – encrypt the connection.

However, what if you want to use auth_pam, and avoid cleartext passwords all together?

If you try to connect to MySQL using Python, you will receive this error: “Client does not support authentication protocol requested by server; consider upgrading MySQL client.”

Back in 2013, Percona posted about how to install and configure auth_pam and auth_pam_compat. The article explains how to recompile clients to get them to work:

The good news is that if the client uses libmysqlclient library to connect via MySQL, you can recompile the client’s source code to use the libmysqlclient library of Percona Server to make it compatible. This involves installing Percona Server development library, compiler tools, and development libraries followed by compiling and installing the client’s source code.

The Hitch


The hitch with Python is that there are a few different ways to connect to MySQL with Python. In fact, MySQL has written a Python connector, called mysql-connector-python. According to the documentation for mysql-connector-python:

It is written in pure Python and does not have any dependencies except for the Python Standard Library.

This means we cannot recompile mysql-connector-python to use the libmysqlclient library from Percona that supports auth_pam – because it does not use the libmysqlclient library.

However, mysql-connector-python is not the only way to connect MySQL to python. There is a mysqlclient-python package, which provides the MySQLdb module for connecting to MySQL. According to the documentation:

MySQLdb is a thin Python wrapper around _mysql

And the docs for the _mysql module say:

_mysql provides an interface which mostly implements the MySQL C API.

It is using the standard library, and we can recompile it. Here is a mirror of the Perl recompilation process for MySQL.

Recompiling MySQLdb to support auth_pam

Step 1

“Install Percona yum repository and Percona Server development library.” This is not a problem, do what you need to do to install Percona-Server-devel for your version.

Step 2

Install a package manager so you can build a package – optional, but useful, if you ever want to have this new client without having to recompile. As in the example, I chose the RPM package manager, so I installed rpm-build.

Step 3

“Download and install the source RPM for the client package.”

I did a web search for “mysqlclient-python source rpm” and found the rpmfind page containing many versions. If you click on the link in the “Package” column you will get to a page that has a link for the Source RPM. I chose the most recent (as of this writing) CentOS package.

So I downloaded the source RPM and installed it into the sources directory:

cd SRPMS
wget http://vault.centos.org/7.4.1708/os/Source/SPackages/MySQL-python-1.2.5-1.el7.src.rpm
cd ../SOURCES
rpm -Uvh MySQL-python-1.2.5-1.el7.src.rpm

This unpacks MySQL-python-1.2.5.zip and a patch file in the SOURCES directory and puts a spec file in the SPECS directory, so this is not as complicated as the PHP version.

Step 4

“Install compilers and dependencies”.
On my host I had no work to get any requirements installed (your mileage may vary – I had installed a lot of dependencies previously in my PHP test, and used the same machine). Make sure to include the Percona Server package for the /usr/lib64/mysql/plugin/dialog.so file:
yum install Percona-Server-server-55-5.5.55-rel38.8.el6.x86_64

Step 5

“Build the RPM file”.


rpmbuild -bb rpmbuild/SPECS/MySQL-python.spec

Then I installed my new package and tested it, and it worked!
# rpm -e MySQL-python
# rpm -Uvh /root/rpmbuild/RPMS/x86_64/MySQL-python-1.2.5-1.el6.x86_64.rpm
Preparing… ########################################### [100%]
1:MySQL-python ########################################### [100%]

I will not be continuing this experiment with any other clients (e.g. not going to try for Ruby) but I welcome others to do the same!

4 responses to “LDAP with auth_pam and Python to authenticate against MySQL

  1. Pingback: LDAP with auth_pam and PHP to authenticate against MySQL | Sheeri Dot Com

  2. this is fine for human users, but as soon as you tie an application that doesn’t behave as well as it should with connects/reconnects to LDAP, it’s not likely to go well since auth doesn’t happen against local tables that are cached anymore, but handed off to another daemon that can fail (we’ve seen sssd fail under heavy IO)

    also, pam auth plugin (at least in mariadb) breaks the init script because of how init scrit uses “UNKNOWN_MYSQL_USER” for the ping command to determine up/down state without having to auth. pam_auth forces that to look the user up in LDAP

    • Gurov, these are great points. I am of the opinion that LDAP should be used for human users, not role users. I also feel anything automated or application-based should have its own secure password, changed regularly.

  3. Also I am not surprised it breaks in MariaDB – it’s a Percona plugin, so it may also break Oracle’s MySQL. I have not tested on that.