libtacplus(3)

NAME

libtacplus - TACACS+ client library

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
authentication, authorization, and accounting by means of network re
quests 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 vir
tual 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 configuration 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 configuration file /etc/tacplus.conf is used. tac_config() re
turns 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 ad
dress 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 sin; gle connection
mode when communicating with the server. In; single connection mode, the original TCP connection is held; open for multiple 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 oc
curs.
tac_add_server() may be called multiple times, and it may be
used
together with tac_config(). At most 10 servers may be spec
ified. 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 argu
ments must be set to appropriate values as defined in the TACACS+ protocol
specification.
The #include <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 argu
ments must be set to appropriate values as defined in the TACACS+ protocol
specification.
The #include <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 creates its own copies of any strings provided to these func
tions, so that it is not necessary for the caller to preserve them. By de
fault, 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 ef
fectively
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 construct
ed, 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 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 con
tain 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 dynamically-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 ter
minated 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 re
ceived 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 ad
ditional information 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 on
ly 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 re
ceived from the server.

SENDING THE AUTHORIZATION REQUEST AND RECEIVING THE RESPONSE

After the TACACS+ authorization request has been construct
ed, 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 in
clude:: 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 re
sponse packet from the server may contain a server message, a data string,
or both. Refer to EXTRACTING INFORMATION FROM THE SERVER'S AUTHENTI
CATION 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 dynamically-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 ter
minated 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 re
trieved by calling 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 handle.

CLEANUP

To free the resources used by the TACACS+ library, call
tac_close().

RETURN VALUES

The following functions return a non-negative value on suc
cess. 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 suc
cess. If they are unable to allocate sufficient virtual memory, they re
turn NULL and record an error message which can be retrieved using
tac_strerror().: tac_get_av()
tac_get_av_pair()
tac_get_data()
tac_get_msg()
The following functions return a non-NULL pointer on suc
cess. If they are unable to allocate sufficient virtual memory, they re
turn NULL, without recording an error message.: tac_open()

FILES

/etc/tacplus.conf

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

docs.sk

comprehensive documentation repository

See also

libtacplus(3)

NAME

SYNOPSIS

DESCRIPTION

INITIALIZATION

CREATING A TACACS+ AUTHENTICATION REQUEST

CREATING A TACACS+ AUTHORIZATION REQUEST

SETTING OPTIONAL PARAMETERS ON A REQUEST

SENDING THE AUTHENTICATION REQUEST AND RECEIVING THE RESPONSE

EXTRACTING INFORMATION FROM THE SERVER'S AUTHENTICATION RESPONSE

SENDING AUTHENTICATION CONTINUE PACKETS

SENDING THE AUTHORIZATION REQUEST AND RECEIVING THE RESPONSE

TAC_AUTHEN_AV_COUNT

EXTRACTING INFORMATION FROM THE SERVER'S AUTHORIZATION RESPONSE

OBTAINING ERROR MESSAGES

CLEANUP

RETURN VALUES

FILES

SEE ALSO

AUTHORS