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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_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 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

     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_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_pair()
	   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 ALSO

     tacplus.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.

FreeBSD 5.4		       September 2, 1998		   FreeBSD 5.4

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