.\"	$NetBSD: libsaslc.3,v 1.16 2015/07/13 13:57:44 shm Exp $
.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Mateusz Kocielski.
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.Dd May 3, 2015
.Dt LIBSASLC 3
.Os
.Sh NAME
.Nm libsaslc ,
.Nm saslc.d ,
.Nm saslc_alloc ,
.Nm saslc_end ,
.Nm saslc_init ,
.Nm saslc_sess_init ,
.Nm saslc_sess_end ,
.Nm saslc_sess_getprop ,
.Nm saslc_sess_setprop ,
.Nm saslc_sess_cont ,
.Nm saslc_sess_decode ,
.Nm saslc_sess_encode ,
.Nm saslc_sess_getmech ,
.Nm saslc_sess_strerror ,
.Nm saslc_strerror
.Nd Simple Authentication and Security Layer client library
.Sh LIBRARY
.Lb libsaslc
.Sh SYNOPSIS
.In saslc.h
.Ft saslc_t *
.Fn saslc_alloc "void"
.Ft int
.Fn saslc_end "saslc_t *ctx"
.Ft int
.Fn saslc_init "saslc_t *ctx" "const char *appname" "const char *cfgpath"
.Ft saslc_sess_t *
.Fn saslc_sess_init "saslc_t *ctx" "const char *mechs" "const char *secopts"
.Ft void
.Fn saslc_sess_end "saslc_sess_t *sess"
.Ft const char *
.Fn saslc_sess_getprop "saslc_sess_t *sess" "const char *key"
.Ft int
.Fn saslc_sess_setprop "saslc_sess_t *sess" "const char *key" \
"const char *value"
.Ft int
.Fn saslc_sess_cont "saslc_sess_t *sess" "const void *in" "size_t inlen" \
"void* *out" "size_t *outlen"
.Ft ssize_t
.Fn saslc_sess_decode "saslc_sess_t *sess" "const void *in" "size_t inlen" \
"void* *out" "size_t *outlen"
.Ft ssize_t
.Fn saslc_sess_encode "saslc_sess_t *sess" "const void *in" "size_t inlen" \
"void* *out" "size_t *outlen"
.Ft const char *
.Fn saslc_sess_getmech "saslc_sess_t *sess"
.Ft const char *
.Fn saslc_sess_strerror "saslc_sess_t *sess"
.Ft const char *
.Fn saslc_strerror "saslc_t *ctx"
.Sh DESCRIPTION
The
.Nm libsaslc
library offers a client interface for the
Simple Authentication and Security Layer
.Pq Tn SASL .
The library is heavily influenced by its use with
.Xr postfix 1 .
.Sh FUNCTIONS
The following functions are available in the library.
.Bl -tag -width compact
.It Fn saslc_alloc ""
The
.Fn saslc_alloc
function allocates and returns a new saslc context.
The context is uninitialized: see
.Fn saslc_init .
Returns
.Dv NULL
on error.
.It Fn saslc_end "ctx"
The
.Fn saslc_end
function destroys and deallocate resources used by the context
.Ar ctx .
The context shouldn't have any sessions assigned to it.
Returns 0 on success and \-1 if the context has active sessions and
cannot be deallocated.
.It Fn saslc_init "ctx" "appname" "cfgpath"
The
.Fn saslc_init
function initializes the saslc context
.Ar ctx .
Based on the application name
.Ar appname ,
it also parses the configuration files as indicated by
.Ar cfgpath ,
sets up the context and mechanism dictionaries, and creates mechanism
list for the context.
If
.Ar cfgpath
is
.Dv NULL ,
it checks the environment variable
.Ev SASLC_CONFIG
for a location and if that is not found it uses the default path
.Pa /etc/saslc.d .
Returns 0 on success and \-1 on failure.
.It Fn saslc_sess_init "ctx" "mechs" "secopts"
The
.Fn saslc_sess_init
function creates new session assigned to the
.Ar ctx
context.
The function chooses the mechanism to use for authentication from the
.Ar mechs
list taking into account the requirements from the
.Ar secopts
list.
Both lists may be space or comma delimited.
The first matching mechanism from the
.Ar mechs
list is used.
See
.Sx CONFIGURATION
below for the supported mechanisms.
The valid security options are
.Pp
.Bl -tag -width "nodictionaryxxx" -offset indent -compact
.It Qo noanonymous Qc
reject anonymous mechanisms
.It Qo noplaintext Qc
reject plaintext mechanisms
.It Qo nodictionary Qc
reject mechanisms prone to dictionary attack
.It Qo noactive Qc
reject mechanisms prone to active non-dictionary attacks
.It Qo mutual Qc
require mutual authentication mechanisms
.El
.Pp
Unknown security options are ignored.
Returns a session handle or
.Dv NULL
on error or no match.
.It Fn saslc_sess_end "sess"
The
.Fn saslc_sess_end
function ends the sasl session
.Ar sess .
It destroys and deallocates all internal resources.
This does not fail.
.It Fn saslc_sess_getprop "sess" "key"
The
.Fn saslc_sess_getprop
function gets the property indicated by the
.Ar key
from the saslc dictionaries.
Dictionaries are searched in following order: session
.Ar sess
dictionary,
context dictionary (global configuration), and mechanism dictionary.
Returns the property value or
.Dv NULL
if the property is not found.
.It Fn saslc_sess_setprop "sess" "key" "value"
The
.Fn saslc_sess_setprop
function sets the property indexed by
.Ar key
to the value
.Ar value
in the session
.Ar sess
dictionary.
If the property already exists in the session dictionary, then the
previous value is replaced by the new value.
If
.Ar value
is
.Dv NULL ,
then any previous value in the session dictionary is removed.
Returns 0 on success or \-1 on failure.
.It Fn saslc_sess_cont "sess" "in" "inlen" "out" "outlen"
The
.Fn saslc_sess_cont
function performs one step of the sasl authentication.
It reads
.Ar inlen
bytes of input data
.Pq from the server
from the
.Ar in
buffer and stores
.Ar outlen
bytes of output data in
.Ar out
.Pq for the server .
The user is responsible for freeing memory allocated for
.Ar out .
It returns 0 if the authentication process is completed, 1 if another
step is required, and \-1 on error.
Note that the completion of authentication process does not mean the
client is authenticated; that is determined by the server.
.It Fn saslc_sess_decode "sess" "in" "inlen" "out" "outlen"
The
.Fn saslc_sess_encode
and
.Fn saslc_sess_decode
functions are used to provide the integrity
.Pq Qq auth-int
and  confidentiality
.Pq Qq auth-conf
layers for mechanisms that provide them.
They encode and, respectively, decode
.Ar inlen
bytes of data from the
.Ar in
buffer using the method negotiated during authentication.
On error they return \-1.
Otherwise, they return the number of bytes consumed from
.Ar in
and output
.Ar outlen
bytes of data in the
.Ar out
buffer.
The user is responsible for freeing memory allocated for
.Ar out .
If
.Ar outlen
is 0, more data is needed before anything can be output.
Unused input data is stored internally for use in subsequent calls.
.Pp
When decoding, the internal buffers can only be flushed by providing
the missing packet data and it is an error to call
.Fn ssalc_sess_decode
with
.Ar inlen
= 0.
The first call of
.Fn saslc_sess_decode
in a session must begin at the start of a packet.
Subsequent calls need not be aligned on packet boundaries.
.It Fn saslc_sess_encode "sess" "in" "inlen" "out" "outlen"
As described above,
.Fn saslc_sess_encode
encodes
.Ar inlen
bytes of data from the
.Ar in
buffer.
Note that unlike when decoding,
the internal buffer may be flushed through the encoder
by calling
.Fn saslc_sess_encode
with
.Ar inlen
= 0.
In this case,
.Fn saslc_sess_encode
returns the number of bytes that were flushed from the internal buffer.
.It Fn saslc_sess_getmech "sess"
The
.Fn saslc_sess_getmech
function returns the name of the mechanism used in the session
.Fa sess .
The function does not fail.
.It Fn saslc_sess_strerror "sess"
The
.Fn saslc_sess_strerror
returns the error message associated with the session
.Fa sess .
.It Fn saslc_strerror "ctx"
The
.Fn saslc_strerror
function operates as
.Fn saslc_sess_strerror ,
but instead returns the error message string for the last error in the context
.Fa ctx .
Neither function will ever return
.Dv NULL .
.El
.Sh CONFIGURATION
The library uses three types of dictionaries: context (or global),
session, and mechanism, and they are searched in that order by
.Fn saslc_getprop
and the first matching entry is taken.
The context and mechanism dictionaries are loaded from configuration
files, while the session dictionary is loaded by the caller via
.Fn saslc_setprop .
.Pp
The configuration file
.Pa <cfgpath>/<appname>/saslc.conf
is used for the context configuration.
The
.Pa <cfgpath>/<appname>/mech/<mechanism>.conf
file is used for the mechanism configuration.
The
.Pa <cfgpath>
is
.Pa /etc/saslc.d
by default, but this may be overridden by the environment variable
.Ev SASLC_CONFIG ,
which in turn may be overridden by
.Fn saslc_init .
The
.Pa <appname>
is
.Pa saslc
by default, but may also be overridden by
.Fn saslc_init .
Finally, the
.Pa <mechanism>
is the mechanism in use by the session as returned by
.Fn saslc_sess_getmech .
Note that this name is case sensitive.
The currently supported mechanisms are
.Bl -tag -width DIGEST-MD5 -offset indent
.It ANONYMOUS
See RFC 2245 and RFC 4505.
.It CRAM-MD5
See RFC 2195.
.It DIGEST-MD5
See RFC 2831.
.It EXTERNAL
See RFC 2222 section 7.4 and RFC 4422 appendix A.
.It GSSAPI
See RFC 2222 section 7.2 and RFC 4752.
This requires GSS, Heimdal, or MIT Kerberos.
.It LOGIN
Non-standard, but common.
.It PLAIN
See RFC 2595 and RFC 4616.
.El
.Pp
If any of the mechanism files are missing they are silently ignored,
unless debugging is enabled.
.Pp
The configuration files consists of lines of the form:
.Bd -literal -offset indent
\fB#\fP comment line
.Ao key Ac \~\~ Ao value Ac \~\~ Bo \fB#\fP comment Bc
.Ed
.Pp
The
.Aq key
is a string beginning with an alpha character
.Pq Xr isalpha 3
followed by any number of alpha numeric
.Pq Xr isalnum 3
or underscore
.Sq _
characters; this is case sensitive.
The
.Aq value
is a number or a quoted string.
More than one
.Aq key
and
.Aq value
pair may occur on a single line, but they may not be broken across
lines.
A
.Sq \fB#\fP
character
.Pq outside a quoted string
indicates that the rest of the line is a comment.
.Pp
NOTE: Currently, no escaping is supported in strings, so they may not
contain quotes.
Numbers must be between 0 and
.Dv LLONG_MAX ,
inclusive.
Any base supported by
.Xr strtoll 3
is allowed.
.Sh PROPERTIES
Most of the control of the library
behavior is done via setting various properties in the context or
mechanism dictionaries via the configuration files or in the session
dictionary with
.Fn saslc_setprop .
The following properties are currently used, as defined in
.Pa saslc.h :
.Bl -tag -width indent
.It SASLC_PROP_AUTHCID Po Qo AUTHCID Qc Pc
The authentication name
.Pq or username
to authenticate with.
Used by all mechanisms except EXTERNAL.
.It SASLC_PROP_AUTHZID Po Qo AUTHZID Qc Pc
The authorization string to use.
By default, this string is empty.
Used by the DIGEST-MD5, EXTERNAL, and PLAIN mechanisms.
.It SASLC_PROP_BASE64IO Po Qo BASE64IO Qc Pc
If true ("true", "yes", or nonzero), then input and output strings are
base64 encoded.
Any other value is false and the input and output strings are not
base64 encoded.
By default, this is assumed true.
Used by all mechanisms.
.It SASLC_PROP_CIPHERMASK Po Qo CIPHERMASK Qc Pc
The mask of ciphers to use with the DIGEST-MD5 mechanism when using
the
.Qq auth-conf
QOP.
By default all supported ciphers are used, but they may be limited by
a comma delimited list of cipher names.
The recognized cipher names for DIGEST-MD5 are:
.Pp
.Bl -tag -offset indent -compact
.It Li "3des"
Triple-DES Cipher in CBC "two keys" mode with 112 bit key
.It Li "aes"
AES Cipher in CBC mode with 128 bit key
.It Li "des"
DES Cipher in CBC mode with 56 bit key
.It Li "rc4"
RC4 Cipher with 128 bit key
.It Li "rc4-40"
RC4 Cipher with 40 bit key
.It Li "rc4-56"
RC4 Cipher with 56 bit key
.El
.Pp
The default value is
.Qq des,3des,rc4,rc4_40,rc4_56,aes .
.Po
Note that
.Qq aes
is not part of the official standard.
.Pc
Used by the DIGEST-MD5 mechanism.
.It SASLC_PROP_DEBUG Po Qo DEBUG Qc Pc
If true, then enable debug messages.
This is implemented as a global variable so it will affect all
sessions.
If set via
.Fn saslc_sess_setprop ,
it should be set before the first call to
.Fn saslc_sess_cont .
.Po
Also see the environment variable
.Ev SASLC_ENV_DEBUG
in the
.Sx ENVIRONMENT
section below.
.Pc
.It SASLC_PROP_HOSTNAME Po Qo HOSTNAME Qc Pc
The fully qualified domain name of the server host.
Used by the DIGEST-MD5 and GSSAPI mechanisms.
.It SASLC_PROP_MAXBUF Po Qo MAXBUF Qc Pc
The size of the decode buffer.
This info is sent to the server so that it doesn't send packets that
won't fit in the decode buffer when decoded.
Used by the DIGEST-MD5 and GSSAPI mechanisms.
.It SASLC_PROP_PASSWD Po Qo PASSWD Qc Pc
The password to authenticate with.
Used by the CRAM-MD5, DIGEST-MD5, LOGIN, and PLAIN mechanisms.
.It SASLC_PROP_QOPMASK Po Qo QOPMASK Qc Pc
The mask of QOP (quality of protection) to use with the DIGEST-MD5
and GSSAPI mechanisms.
By default all supported QOP values are allowed, but they may be
limited by a comma delimited list of QOP values.
The recognized QOP values are:
.Pp
.Bl -tag -offset indent -compact
.It Li "auth"
authentication only
.It Li "auth-int"
authentication with integrity
.It Li "auth-conf"
authentication with confidentiality
.El
.Pp
so the default value of the mask is
.Qq auth,auth-int,auth-conf .
Used by the DIGEST-MD5 and GSSAPI mechanisms.
.It SASLC_PROP_REALM Po Qo REALM Qc Pc
A comma delimited list of possible realms to use for authentication.
The format of each element in the list is
.Qq Oo Ao hostname Ac : Oc Ns Ao realm Ac .
The user specified realm is the first realm in the list with a
matching hostname or, if none is found, the first realm in the list
with no hostname.
If the server provides a list of realms, the one matching the user
specified realm is selected.
If no match is found or if the user didn't provide a realm, the first
realm provided by the server is selected.
If the server doesn't provide any realms, use the user specified realm
if there is one, or the hostname if not.
This is useful when the server provides multiple realms or no realm.
Used by the DIGEST-MD5 mechanism.
.It SASLC_PROP_SECURITY Po Qo SECURITY Qc Pc
A comma delimited list of extra security option flags that will be
.Qo or Qc Ns -ed
together with those passed to
.Fn saslc_sess_init .
Since these flags are used to choose the session mechanism, they are
only effective if they are in the context configuration file.
.Po
See the
.Sx CONFIGURATION
section and the
.Fn saslc_sess_init
function.
.Pc
.It SASLC_PROP_SERVICE Po Qo SERVICE Qc Pc
The service being used, e.g., smtp, imap, etc.
Used by the DIGEST-MD5 and GSSAPI mechanisms.
.It SASLC_PROP_SERVNAME Po Qo SERVNAME Qc Pc
A comma delimited list of possible service names with elements of the
form
.Qq Oo Ao hostname Ac : Oc Ns Ao serv-name Ac
and with the same rules as for the SASLC_PROP_REALM list.
This should only be used if the client uses a DNS name for the service
that is different from the FQDN of the server.
For example, the service name
.Em example.com
might resolve
.Pq via SRV or MX records
into a set of other DNS names, one of which,
.Em mail3.example.com ,
is the FQDN of the server.
.Po
See RFC 2831 section 2.1.2
.Qq serv-name .
.Pc
Used by the DIGEST-MD5 mechanism.
.El
.Pp
The defines in
.Pa saslc.h
should be used in code, but their values need to be used in the config
files.
.Sh ENVIRONMENT
The following environment variables
.Pq defined in Pa saslc.h
affect the behavior of the library:
.Bl -tag -width indent
.It Ev SASLC_ENV_CONFIG Po Qo SASLC_CONFIG Qc Pc
If the environment variable
.Ev SASLC_CONFIG
is set it overrides the default configuration file location of
.Pa /etc/saslc.d .
This may be overridden by
.Fn saslc_init .
.It Ev SASLC_ENV_DEBUG Po Qo SASLC_DEBUG Qc Pc
If set, turn on debugging messages.
This turns on debugging as early as possible and is a global setting.
.El
.Sh GSSAPI AND KERBEROS
The following is a minimal
.Pq Heimdal
Kerberos 5 setup for use with an smtp server that has been configured
to support
.Em SASL
with the
.Em GSSAPI
mechanism.
It assumes that Kerberos and the smtp server will both run on
.Em server.my.domain
and that the client is on
.Em client.my.domain .
It also assumes that the smtp server runs as user
.Em postfix
and group
.Em mail ,
and that it is not chrooted.
.Pp
On
.Em server.my.domain
run the following script as
.Em root
and then start the Kerberos server
.Xr kdc 8 .
You will be prompted for a master password for Kerberos and a password
for the
.Em postfix
principal.
.Bd -literal -offset indent
#/bin/sh
.Pp
cat <<- EOF >> /etc/krb5.conf
[libdefaults]
	default_realm = MY.DOMAIN
[realms]
	MY.DOMAIN = {
		kdc = server.my.domain
		admin_servers = server.my.domain
	}
[domain_realm]
	.my.domain = MY.DOMAIN
EOF
.Pp
mkdir /var/heimdal
chown root:wheel /var/heimdal
chmod 755 /var/heimdal
.Pp
kstash
kadmin -l init --realm-max-ticket-life=unlimited \\
               --realm-max-renewable-life=unlimited \\
               MY.DOMAIN
kadmin -l add  --max-ticket-life="1 day" \\
               --max-renewable-life="1 week" \\
               --expiration-time=never \\
               --pw-expiration-time=never \\
               --attributes="" \\
               postfix
kadmin -l add  --random-key \\
               --max-ticket-life="1 day" \\
               --max-renewable-life="1 week" \\
               --expiration-time=never \\
               --pw-expiration-time=never \\
               --attributes="" \\
               smtp/server.my.domain
kadmin -l ext -k /etc/krb5.keytab smtp/server.my.domain
chown root:mail /etc/krb5.keytab
chmod 640 /etc/krb5.keytab
.Ed
.Pp
Note that the keytab
.Pa /etc/krb5.keytab
must be readable by the smtp server or authentication will fail.
The location of this keytab file may be changed with the environment
variable
.Ev KRB5_KTNAME .
If postfix is the smtp server, note the
.Em import_environment
parameter
.Pq see Xr postconf 5 .
.Pp
On
.Em client.my.domain
copy the keytab file from
.Pa server.my.domain:/etc/krb5.keytab
to
.Pa /etc/krb5.keytab .
Setup the
.Pa /etc/saslc.d
configuration directory
.Po see Sx CONFIGURATION
above
.Pc .
Add the line
.Bd -literal -offset indent
AUTHCID		"postfix"
.Ed
.Pp
to the file
.Pa /etc/saslc.d/postfix/mech/GSSAPI.conf
so that the
.Em postfix
principal will be used for authentication.
Enable
.Em SASL
in the smtp client.
Assuming the smtp client is postfix, you will need to add the
following to the
.Pa /etc/postfix/main.cf
file to do this:
.Bd -literal -offset indent
smtp_sasl_auth_enable = yes
smtp_sasl_type = saslc
smtp_sasl_mechanism_filter = GSSAPI
relayhost = [server.my.domain]:submission
.Ed
.Pp
Here we have assumed the
.Em submission
port is the port the server is listening to.
Finally, as
.Em root ,
run the command
.Bd -literal -offset indent
su -m postfix -c kinit
.Ed
.Pp
to obtain a ticket for the postfix user with the postfix credential
and you should be good to go!
.Sh FILES
.Bl -tag -width /etc/saslc.d
.It Pa /etc/saslc.d
.El
.Sh EXAMPLES
The following code fragments illustrate the possible use of the
functions described above.
.Bd -literal
int
decode_stream(saslc_sess_t *sess, int fdin, int fdout)
{
	uint8_t buf[BUFSIZE];
	uint8_t *in;
	void *out;
	size_t inlen, outlen;
	ssize_t n, rval;
.Pp
	for (;;) {
		if ((rval = read(fdin, buf, sizeof(buf))) == \-1)
			return \-1;
		if (rval == 0)
			break;
		in = buf;
		inlen = rval;
		while (inlen > 0) {
			rval = saslc_sess_decode(sess, in, inlen, &out,
			    &outlen);
			if (rval == \-1)
				return \-1;
			if (outlen > 0) {
				n = write(fdout, out, outlen);
				free(out);
				if (n == \-1)
					return \-1;
			}
			in += rval;
			inlen -= rval;
		}
	}
	return 0;
}
.Pp
int
encode_stream(saslc_sess_t *sess, int fdin, int fdout)
{
	uint8_t buf[BUFSIZE];
	uint8_t *in;
	void *out;
	size_t inlen, outlen;
	ssize_t n, rval;
.Pp
	for (;;) {
		if ((rval = read(fdin, buf, sizeof(buf))) == \-1)
			return \-1;
		if (rval == 0)
			break;
		in = buf;
		inlen = rval;
		while (inlen > 0) {
			rval = saslc_sess_encode(sess, in, inlen, &out,
			    &outlen);
			if (rval == \-1)
				return \-1;
			if (outlen > 0) {
				n = write(fdout, out, outlen);
				free(out);
				if (n == \-1)
					return \-1;
			}
			in += rval;
			inlen -= rval;
		}
	}
	/* flush internal encoder buffer */
	if (saslc_sess_encode(sess, NULL, 0, &out, &outlen) == \-1)
		return \-1;
	if (outlen > 0)
		if (write(fdout, out, outlen) == \-1)
			return \-1;
	return 0;
}
.Ed
.Sh COMPATIBILITY
There exist other SASL client library implementations including Cyrus SASL
(http://asg.web.cmu.edu/sasl/sasl-library.html) and GNU SASL
(http://www.gnu.org/software/gsasl/).
.Sh STANDARDS
RFC 2195, RFC 2222, RFC 2245, RFC 2595, RFC 2831, RFC 4422, RFC 4505,
RFC 4616, RFC 4752.
.Sh HISTORY
The
.Nm
library appeared in
.Nx 6.0 .
.Sh CAVEATS
The API was heavily influenced by its use with
.Xr postfix 1 .
.Pp
Currently the ANONYMOUS, LOGIN, PLAIN, CRAM-MD5, DIGEST-MD5, and
GSSAPI mechanisms have been tested and shown to work for
authentication with a
.Xr postfix 1
SMTP server using the cyrus-sasl library.
LOGIN, PLAIN, CRAM-MD5, and DIGEST-MD5 have also been tested and shown
to work with a
.Xr postfix 1
SMTP server using a dovecot backend for authentication.
The DIGEST-MD5 and GSSAPI specs also provide for integrity and
confidentiality layers via the
.Fn saslc_sess_encode
and
.Fn saslc_sess_decode
routines, but these have not yet been tested against any servers.