Warning

mod_session_dbd DBD/SQL based session support Extension mod_session_dbd.c session_dbd_module Available in Apache 2.3 and later

Warning

The session modules make use of HTTP cookies, and as such can fall victim to Cross Site Scripting attacks, or expose potentially private information to clients. Please ensure that the relevant risks have been taken into account before enabling the session functionality on your server.

This submodule of mod_session provides support for the storage of user sessions within a SQL database using the mod_dbd module.

Sessions can either be anonymous, where the session is keyed by a unique UUID string stored on the browser in a cookie, or per user, where the session is keyed against the userid of the logged in user.

SQL based sessions are hidden from the browser, and so offer a measure of privacy without the need for encryption.

Different webservers within a server farm may choose to share a database, and so share sessions with one another.

For more details on the session interface, see the documentation for the mod_session module.

mod_session mod_session_crypto mod_session_cookie mod_dbd

DBD Configuration

Before the mod_session_dbd module can be configured to maintain a session, the mod_dbd module must be configured to make the various database queries available to the server.

There are four queries required to keep a session maintained, to select an existing session, to update an existing session, to insert a new session, and to delete an expired or empty session. These queries are configured as per the example below.

Sample DBD configuration DBDriver pgsql
DBDParams "dbname=apachesession user=apache password=xxxxx host=localhost"
DBDPrepareSQL "delete from session where key = %s" deletesession
DBDPrepareSQL "update session set value = %s, expiry = %lld where key = %s" updatesession
DBDPrepareSQL "insert into session (value, expiry, key) values (%s, %lld, %s)" insertsession
DBDPrepareSQL "select value from session where key = %s and (expiry = 0 or expiry > %lld)" selectsession
DBDPrepareSQL "delete from session where expiry != 0 and expiry < %lld" cleansession

Anonymous Sessions

Anonymous sessions are keyed against a unique UUID, and stored on the browser within an HTTP cookie. This method is similar to that used by most application servers to store session information.

To create a simple anonymous session and store it in a postgres database table called apachesession, and save the session ID in a cookie called session, configure the session as follows:

SQL based anonymous session Session On
SessionDBDCookieName session path=/

For more examples on how the session can be configured to be read from and written to by a CGI application, see the mod_session examples section.

For documentation on how the session can be used to store username and password details, see the mod_auth_form module.

Per User Sessions

Per user sessions are keyed against the username of a successfully authenticated user. It offers the most privacy, as no external handle to the session exists outside of the authenticated realm.

Per user sessions work within a correctly configured authenticated environment, be that using basic authentication, digest authentication or SSL client certificates. Due to the limitations of who came first, the chicken or the egg, per user sessions cannot be used to store authentication credentials from a module like mod_auth_form.

To create a simple per user session and store it in a postgres database table called apachesession, and with the session keyed to the userid, configure the session as follows:

SQL based per user session Session On
SessionDBDPerUser On

Database Housekeeping

Over the course of time, the database can be expected to start accumulating expired sessions. At this point, the mod_session_dbd module is not yet able to handle session expiry automatically.

Warning

The administrator will need to set up an external process via cron to clean out expired sessions.

SessionDBDCookieName Name and attributes for the RFC2109 cookie storing the session ID SessionDBDCookieName name attributes none server config virtual host directory .htaccess

The SessionDBDCookieName directive specifies the name and optional attributes of an RFC2109 compliant cookie inside which the session ID will be stored. RFC2109 cookies are set using the Set-Cookie HTTP header.

An optional list of cookie attributes can be specified, as per the example below. These attributes are inserted into the cookie as is, and are not interpreted by Apache. Ensure that your attributes are defined correctly as per the cookie specification.

Cookie with attributes Session On
SessionDBDCookieName session path=/private;domain=example.com;httponly;secure;version=1;
SessionDBDCookieName2 Name and attributes for the RFC2965 cookie storing the session ID SessionDBDCookieName2 name attributes none server config virtual host directory .htaccess

The SessionDBDCookieName2 directive specifies the name and optional attributes of an RFC2965 compliant cookie inside which the session ID will be stored. RFC2965 cookies are set using the Set-Cookie2 HTTP header.

Cookie2 with attributes Session On
SessionDBDCookieName2 session path=/private;domain=example.com;httponly;secure;version=1;
SessionDBDCookieRemove Control for whether session ID cookies should be removed from incoming HTTP headers SessionDBDCookieRemove On|Off SessionDBDCookieRemove On server config virtual host directory .htaccess

The SessionDBDCookieRemove flag controls whether the cookies containing the session ID will be removed from the headers during request processing.

In a reverse proxy situation where the Apache server acts as a server frontend for a backend origin server, revealing the contents of the session ID cookie to the backend could be a potential privacy violation. When set to on, the session ID cookie will be removed from the incoming HTTP headers.

SessionDBDPerUser Enable a per user session SessionDBDPerUser On|Off SessionDBDPerUser Off server config virtual host directory .htaccess

The SessionDBDPerUser flag enables a per user session keyed against the user's login name. If the user is not logged in, this directive will be ignored.

SessionDBDSelectLabel The SQL query to use to select sessions from the database SessionDBDSelectLabel label SessionDBDSelectLabel selectsession server config virtual host directory .htaccess

The SessionDBDSelectLabel directive sets the default select query label to be used to load in a session. This label must have been previously defined using the DBDPrepareSQL directive.

SessionDBDInsertLabel The SQL query to use to insert sessions into the database SessionDBDInsertLabel label SessionDBDInsertLabel insertsession server config virtual host directory .htaccess

The SessionDBDInsertLabel directive sets the default insert query label to be used to load in a session. This label must have been previously defined using the DBDPrepareSQL directive.

If an attempt to update the session affects no rows, this query will be called to insert the session into the database.

SessionDBDUpdateLabel The SQL query to use to update existing sessions in the database SessionDBDUpdateLabel label SessionDBDUpdateLabel updatesession server config virtual host directory .htaccess

The SessionDBDUpdateLabel directive sets the default update query label to be used to load in a session. This label must have been previously defined using the DBDPrepareSQL directive.

If an attempt to update the session affects no rows, the insert query will be called to insert the session into the database. If the database supports InsertOrUpdate, override this query to perform the update in one query instead of two.

SessionDBDDeleteLabel The SQL query to use to remove sessions from the database SessionDBDDeleteLabel label SessionDBDDeleteLabel deletesession server config virtual host directory .htaccess

The SessionDBDDeleteLabel directive sets the default delete query label to be used to delete an expired or empty session. This label must have been previously defined using the DBDPrepareSQL directive.