LIBTACPLUS(3) BSD Library Functions Manual LIBTACPLUS(3)NAME
libtacplus — TACACS+ client library
LIBRARY
library “libtacplus”
SYNOPSIS
#include <taclib.h>
int
tac_add_server(struct tac_handle *h, const char *host, int port,
const char *secret, int timeout, int flags);
void
tac_clear_avs(struct tac_handle *h);
void
tac_close(struct tac_handle *h);
int
tac_config(struct tac_handle *h, const char *path);
int
tac_create_authen(struct tac_handle *h, int action, int type,
int service);
int
tac_create_author(struct tac_handle *h, int method, int type,
int service);
char *
tac_get_av(struct tac_handle *h, u_int index);
char *
tac_get_av_value(struct tac_handle *h, const char *attribute);
void *
tac_get_data(struct tac_handle *h, size_t *len);
char *
tac_get_msg(struct tac_handle *h);
struct tac_handle *
tac_open(void);
int
tac_send_authen(struct tac_handle *h);
int
tac_send_author(struct tac_handle *h);
int
tac_set_av(struct tac_handle *h, u_int index, const char *av_pair);
int
tac_set_data(struct tac_handle *h, const void *data, size_t data_len);
int
tac_set_msg(struct tac_handle *h, const char *msg);
int
tac_set_port(struct tac_handle *h, const char *port);
int
tac_set_priv(struct tac_handle *h, int priv);
int
tac_set_rem_addr(struct tac_handle *h, const char *addr);
int
tac_set_user(struct tac_handle *h, const char *user);
const char *
tac_strerror(struct tac_handle *h);
DESCRIPTION
The libtacplus library implements the client side of the TACACS+ network
access control protocol. TACACS+ allows clients to perform authentica‐
tion, authorization, and accounting by means of network requests to
remote servers. This library currently supports only the authentication
and authorization portion of the protocol.
INITIALIZATION
To use the library, an application must first call tac_open() to obtain a
struct tac_handle *, which provides context for subsequent operations.
Calls to tac_open() always succeed unless insufficient virtual memory is
available. If the necessary memory cannot be allocated, tac_open()
returns NULL.
Before issuing any TACACS+ requests, the library must be made aware of
the servers it can contact. The easiest way to configure the library is
to call tac_config(). tac_config() causes the library to read a configu‐
ration file whose format is described in tacplus.conf(5). The pathname
of the configuration file is passed as the file argument to tac_config().
This argument may also be given as NULL, in which case the standard con‐
figuration file /etc/tacplus.conf is used. tac_config() returns 0 on
success, or -1 if an error occurs.
The library can also be configured programmatically by calls to
tac_add_server(). The host parameter specifies the server host, either
as a fully qualified domain name or as a dotted-quad IP address in text
form. The port parameter specifies the TCP port to contact on the
server. If port is given as 0, the library uses port 49, the standard
TACACS+ port. The shared secret for the server host is passed to the
secret parameter. It may be any null-terminated string of bytes. The
timeout for receiving replies from the server is passed to the timeout
parameter, in units of seconds. The flags parameter is a bit mask of
flags to specify various characteristics of the server. It may contain:
TAC_SRVR_SINGLE_CONNECT
Causes the library to attempt to negotiate single connection
mode when communicating with the server. In single connec‐
tion mode, the original TCP connection is held open for mul‐
tiple TACACS+ sessions. Older servers do not support this
mode, and some of them become confused if the client attempts
to negotiate it.
tac_add_server() returns 0 on success, or -1 if an error occurs.
tac_add_server() may be called multiple times, and it may be used
together with tac_config(). At most 10 servers may be specified. When
multiple servers are given, they are tried in round-robin fashion until a
working, accessible server is found. Once the library finds such a
server, it continues to use it as long as it works.
CREATING A TACACS+ AUTHENTICATION REQUEST
To begin constructing a new authentication request, call
tac_create_authen(). The action, type, and service arguments must be set
to appropriate values as defined in the TACACS+ protocol specification.
The <taclib.h> header file contains symbolic constants for these values.
CREATING A TACACS+ AUTHORIZATION REQUEST
To begin constructing a new authorization request, call
tac_create_author(). The method, type, and service arguments must be set
to appropriate values as defined in the TACACS+ protocol specification.
The <taclib.h> header file contains symbolic constants for these values.
SETTING OPTIONAL PARAMETERS ON A REQUEST
After creating a request, various optional parameters may be attached to
it through calls to tac_set_av(), tac_set_data(), tac_set_port(),
tac_set_priv(), tac_set_rem_addr(), and tac_set_user(). The library cre‐
ates its own copies of any strings provided to these functions, so that
it is not necessary for the caller to preserve them. By default, each of
these parameters is empty except for the privilege level, which defaults
to ‘USER’ privilege.
tac_set_av() only applies to the context of an authorization request.
The format for an attribute value pair is defined in the TACACS+ protocol
specification. The index specified can be any value between 0 and 255
inclusive and indicates the position in the list to place the attribute
value pair. Calling tac_set_av() with same index twice effectively
replaces the value at that position. Use tac_clear_avs() to clear all
attribute value pairs that may have been set.
SENDING THE AUTHENTICATION REQUEST AND RECEIVING THE RESPONSE
After the TACACS+ authentication request has been constructed, it is sent
by means of tac_send_authen(). This function connects to a server if not
already connected, sends the request, and waits for a reply. On failure,
tac_send_authen() returns -1. Otherwise, it returns the TACACS+ status
code and flags, packed into an integer value. The status can be
extracted using the macro TAC_AUTHEN_STATUS(). Possible status codes,
defined in <taclib.h>, include:
TAC_AUTHEN_STATUS_PASS
TAC_AUTHEN_STATUS_FAIL
TAC_AUTHEN_STATUS_GETDATA
TAC_AUTHEN_STATUS_GETUSER
TAC_AUTHEN_STATUS_GETPASS
TAC_AUTHEN_STATUS_RESTART
TAC_AUTHEN_STATUS_ERROR
TAC_AUTHEN_STATUS_FOLLOW
The only flag is the no-echo flag, which can be tested using the macro
TAC_AUTHEN_NOECHO().
EXTRACTING INFORMATION FROM THE SERVER'S AUTHENTICATION RESPONSE
An authentication response packet from the server may contain a server
message, a data string, or both. After a successful call to
tac_send_authen(), this information may be retrieved from the response by
calling tac_get_msg() and tac_get_data(). These functions return dynami‐
cally-allocated copies of the information from the packet. The caller is
responsible for freeing the copies when it no longer needs them. The
data returned from these functions is guaranteed to be terminated by a
null byte.
In the case of tac_get_data(), the len argument points to a location into
which the library will store the actual length of the received data, not
including the null terminator. This argument may be given as NULL if the
caller is not interested in the length.
SENDING AUTHENTICATION CONTINUE PACKETS
If tac_send_authen() returns a value containing one of the status codes
TAC_AUTHEN_STATUS_GETDATA, TAC_AUTHEN_STATUS_GETUSER, or
TAC_AUTHEN_STATUS_GETPASS, then the client must provide additional infor‐
mation to the server by means of a TACACS+ CONTINUE packet. To do so,
the application must first set the packet's user message and/or data
fields using tac_set_msg() and tac_set_data(). The client then sends the
CONTINUE packet with tac_send_authen(). N.B., tac_create_authen() should
not be called to construct a CONTINUE packet; it is used only for the
initial authentication request.
When it receives the CONTINUE packet, the server may again request more
information by returning TAC_AUTHEN_STATUS_GETDATA,
TAC_AUTHEN_STATUS_GETUSER, or TAC_AUTHEN_STATUS_GETPASS. The application
should send further CONTINUEs until some other status is received from
the server.
SENDING THE AUTHORIZATION REQUEST AND RECEIVING THE RESPONSE
After the TACACS+ authorization request has been constructed, it is sent
by means of tac_send_author(). This function connects to a server if not
already connected, sends the request, and waits for a reply. On failure,
tac_send_author() returns -1. Otherwise, it returns the TACACS+ status
code and number of attribute value (AV) pairs received packed into an
integer value. The status can be extracted using the macro
TAC_AUTHOR_STATUS(). Possible status codes, defined in <taclib.h>,
include:
TAC_AUTHOR_STATUS_PASS_ADD
TAC_AUTHOR_STATUS_PASS_REPL
TAC_AUTHOR_STATUS_FAIL
TAC_AUTHOR_STATUS_ERROR
The number of AV pairs received is obtained using TAC_AUTHEN_AV_COUNT().
EXTRACTING INFORMATION FROM THE SERVER'S AUTHORIZATION RESPONSE
Like an authentication response packet, an authorization response packet
from the server may contain a server message, a data string, or both.
Refer to EXTRACTING INFORMATION FROM THE SERVER'S AUTHENTICATION RESPONSE
for instruction on extraction of those values.
An authorization response packet from the server may also contain
attribute value (AV) pairs. To extract these, use tac_get_av() or
tac_get_av_value(). tac_get_av() takes the index of the AV pair as it is
positioned in the list. The indexes start at 0 (use
TAC_AUTHEN_AV_COUNT() on the return value of tac_send_author() to get the
total number of items in this list). Alternatively, tac_get_av_value()
can be used. tac_get_av_value() takes the attribute name and returns the
corresponding value only, not the AV pair. These functions return dynam‐
ically-allocated copies of the information from the packet. The caller
is responsible for freeing the copies when it no longer needs them. The
data returned from these functions is guaranteed to be terminated by a
null byte.
OBTAINING ERROR MESSAGES
Those functions which accept a struct tac_handle * argument record an
error message if they fail. The error message can be retrieved by call‐
ing tac_strerror(). The message text is overwritten on each new error
for the given struct tac_handle *. Thus the message must be copied if it
is to be preserved through subsequent library calls using the same han‐
dle.
CLEANUP
To free the resources used by the TACACS+ library, call tac_close().
RETURN VALUES
The following functions return a non-negative value on success. If they
detect an error, they return -1 and record an error message which can be
retrieved using tac_strerror().
tac_add_server()tac_config()tac_create_authen()tac_create_author()tac_send_authen()tac_send_author()tac_set_av()tac_set_data()tac_set_msg()tac_set_port()tac_set_priv()tac_set_rem_addr()tac_set_user()
The following functions return a non-NULL pointer on success. If they
are unable to allocate sufficient virtual memory, they return NULL and
record an error message which can be retrieved using tac_strerror().
tac_get_av()tac_get_av_value()tac_get_data()tac_get_msg()
The following functions return a non-NULL pointer on success. If they
are unable to allocate sufficient virtual memory, they return NULL, with‐
out recording an error message.
tac_open()FILES
/etc/tacplus.conf
SEE ALSOtacplus.conf(5)
D. Carrel and Lol Grant, The TACACS+ Protocol, Version 1.78, draft-grant-
tacacs-02.txt (Internet Draft).
AUTHORS
This software was written by John Polstra, and Paul Fraley, and donated
to the FreeBSD project by Juniper Networks, Inc.
BSD September 2, 1998 BSD
