Applications use the SASL library to tell them how to accomplish the SASL protocol exchange, and what the results were.
SASL is only a framework: specific SASL mechanisms govern the exact protocol exchange. If there are n protocols and m different ways of authenticating, SASL attempts to make it so only n plus m different specifications need be written instead of n times m different specifications. With the Cyrus SASL library, the mechanisms need only be written once, and they'll work with all servers that use it.
Applications can set their own proxy policies; by default, the SASL library will only allow the same user to act for another (that is, userid must equal authid).
In the simplest case, a single server on a single machine, the realm might be the fully-qualified domain name of the server. If the applications don't specify a realm to SASL, most mechanisms will default to this.
If a site wishes to share passwords between multiple machines, it might choose it's authentication realm as a domain name, such as "CMU.EDU". On the other hand, in order to prevent the entire site's security from being compromised when one machine is compromised, each server could have it's own realm. Certain mechanisms force the user (client side) to manually configure what realm they're in, making it harder for users to authenticate.
A single site might support multiple different realms. This can confuse applications that weren't written in anticipation of this; make sure your application can support it before adding users from different realms into sasldb with saslpasswd2.
The Kerberos mechanisms treat the SASL realm as the Kerberos realm. Thus, the realm for Kerberos mechanisms defaults to the default Kerberos realm on the server. They may support cross-realm authentication; check your application on how it deals with this.
The principal concern for system administrators is how the authentication identifier and password are verified. The Cyrus SASL library is flexible in this regard:
Saslauthd keeps its named socket in "/var/state/saslauthd" by default. This can be overridden by specifying an alternate value to --with-saslauthd=/foo/bar at compile time, or by passing the -m parameter to saslauthd (along with setting the saslauthd_path SASL option). Whatever directory this is, it must exist in order for saslauthd to function.
Once you configure (and start) saslauthd, there is a testsaslauthd program that can be built with make testsaslauthd in the saslauthd subdirectory of the source. This can be used to check that that the saslauthd daemon is installed and running properly. An invocation like testsaslauthd -u rjs3 -p 1234 with appropriate values for the username and password should do the trick.
If you are using the PAM method to verify passwords with saslauthd, keep in mind that your PAM configuration will need to be configured for each service name that is using saslauthd for authentication. Common service names are "imap", "sieve", and "smtp".
The more flexible and preferred method of adding a routine is to create a new saslauthd mechanism.
The LOGIN mechanism (not to be confused with IMAP4's LOGIN command) is an undocumented, unsupported mechanism. It's included in the Cyrus SASL distribution for the sake of SMTP servers that might want to interoperate with old clients. Do not enable this mechanism unless you know you're going to need it. When enabled, it verifies passwords the same way the PLAIN mechanism does.
There's a downside: in order to verify such responses, the server must keep passwords or password equivalents in a database; if this database is compromised, it is the same as if all the passwords for the realm are compromised.
For simplicity sake, the Cyrus SASL library stores plaintext passwords only in the /etc/sasldb2 database. These passwords are then shared among all mechanisms which choose to use it. Depending on the exact database method used (gdbm, ndbm, or db) the file may have different suffixes or may even have two different files ("sasldb.dir" and "sasldb.pag"). It is also possible for a server to define it's own way of storing authentication secrets. Currently, no application is known to do this.
The principle problem for a system administrator is to make sure that sasldb is properly protected. Only the servers that need to read it to verify passwords should be able to. If there are any normal shell users on the system, they must not be able to read it.
This point is important, so we will repeat it: sasldb stores the plaintext versions of all of its passwords. If it is compromised so are all of the passwords that it stores.
Managing password changes is outside the scope of the library. However, system administrators should probably make a way of letting user's change their passwords available to users. The "saslpasswd2" utility is provided to change the secrets in sasldb. It does not affect PAM, /etc/passwd, or any other standard system library; it only affects secrets stored in sasldb.
Finally, system administrators should think if they want to enable "auto_transition". If set, the library will automatically create secrets in sasldb when a user uses PLAIN to successfully authenticate. However, this means that the individual servers, such as imapd, need read/write access to sasldb, not just read access. By default, "auto_transition" is set to false; set it to true to enable. (There's no point in enabling this option if "pwcheck_method" is "auxprop", and the sasldb plugin is installed)
Applications that wish to use a kerberos mechanism will need access to a service key, stored either in a "srvtab" file (Kerberos 4) or a "keytab" file (Kerberos 5). Currently, the keytab file location is not configurable and defaults to the system default (probably /etc/krb5.keytab).
The Kerberos 4 srvtab file location is configurable; by default it is /etc/srvtab, but this is modifiable by the "srvtab" option. Different SASL applications can use different srvtab files.
A SASL application must be able to read its srvtab or keytab file.
You may want to consult the GSSAPI Tutorial.
OPIE uses its own "opiekeys" database for storing the data necessary for generating the server challenges. The location of the opiekeys file is configurable in SASL; by default it is /etc/opiekeys, but this is modifiable by the "opiekeys" option.
A SASL server application must be able to read and write the opiekeys file.
Note that this means that if your password database is in a SASLdb, and you wish to use it for plaintext password lookups through the sasldb, you will need to set the sasl option pwcheck_method to be auxprop.
By default, the Cyrus SASL library reads it's options from /usr/lib/sasl2/App.conf (where "App" is the application defined name of the application). For instance, Sendmail reads it's configuration from "/usr/lib/sasl2/Sendmail.conf" and the sample server application included with the library looks in "/usr/lib/sasl2/sample.conf".
A standard Cyrus SASL configuration file looks like:
srvtab: /var/app/srvtab pwcheck_method: saslauthd
For instance, Cyrus imapd reads its sasl options from it's own configuration file, /etc/imapd.conf, by prepending all SASL options with "sasl_": the SASL option "pwcheck_method" is set by changing "sasl_pwcheck_method" in /etc/imapd.conf.
don't install a mechanism you aren't going to use.
use --disable-krb4 and --disable-gssapi if you aren't a kerberos site.
use --disable-cram and --disable-digest if you can't use shared secret mechanisms.
need pwcheck? use --enable-pwcheck
what can go wrong with shared libraries?
make sure to make the /usr/lib/sasl symbolic link.
canon_user plugin selection: uses canon_user_plugin option
Unfortunately, since SASL is very flexible (allowing administrators to upgrade and install new authentication plugins without recompiling any applications) its flexibility can also make it a chore to compile.
I'll have some sage advice here when I find some.
A: Check that the srvtab file is readable by the user running as the daemon. For Cyrus imapd, it must be readable by the Cyrus user. By default, the library looks for the srvtab in /etc/srvtab, but it's configurable using the srvtab option.
A: If using OPIE, check that the opiekeys file is readable by the user running the daemon. For Cyrus imapd, it must be readable by the Cyrus user. By default, the library looks for the opiekeys in /etc/opiekeys, but it's configurable using the opiekeys option.
A: Because sasldb now stores plaintext passwords only, the old sasldb is completely incompatible.
A:libsasl reads from /dev/random as part of its initialization. /dev/random is a "secure" source of entropy, and will block your application until a sufficient amount of randomness has been collected to meet libsasl's needs.
To improve performance, you can change DEV_RANDOM in config.h to be /dev/urandom and recompile libsasl. /dev/urandom offers less secure random numbers but should return immediately. The included mechanisms, besides OTP and SRP, use random numbers only to generate nonces, so using /dev/urandom is safe if you aren't using OTP or SRP.
A: sasldb is now a plugin module for the auxprop method.
Make sure you changed the /usr/lib/sasl2/*.conf files to reflect
...and if you're using cyrus-imapd, /etc/imapd.conf must reflect: sasl_pwcheck_method: auxprop
A: The LOGIN mechanism is a non-standard, undocumented plaintext mechanism. It's included in the SASL distribution purely for sites that need it to interoperate with old clients; we don't support it. Don't enable it unless you know you need it.
A: The NTLM mechanism is a non-standard, undocumented mechanism developed by Microsoft. It's included in the SASL distribution purely for sites that need it to interoperate with Microsoft clients (ie, Outlook) and/or servers (ie, Exchange); we don't support it. Don't enable it unless you know you need it.
A: Use the "saslauthd" daemon and setting "pwcheck_method" to "saslauthd".
A: Try setting "CPPFLAGS" and "LDFLAGS" environment variables before running configure, like so:
env CPPFLAGS="-I/usr/local/BerkeleyDB.3.1/include" \ LDFLAGS="-L/usr/local/BerkeleyDB.3.1/lib -R/usr/local/BerkeleyDB.3.1/lib" \ ./configure --with-dblib=berkeley
A: Check syslog output (usually stored in /var/log) for more information. You might want to change your syslog configuration (usually /etc/syslogd.conf) to log "debug.*" to a file while debugging a problem.
The developers make heavy use of strace or truss when debugging a problem that isn't outputting any useful information.
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