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AUTH_OPEN(3) Library Functions Manual AUTH_OPEN(3)

auth_open, auth_call, auth_challenge, auth_check_change, auth_check_expire, auth_clean, auth_close, auth_clrenv, auth_clroption, auth_clroptions, auth_getitem, auth_getpwd, auth_getstate, auth_getvalue, auth_set_va_list, auth_setdata, auth_setenv, auth_setitem, auth_setoption, auth_setpwd, auth_setstate — interface to the BSD Authentication system

#include <sys/types.h>
#include <login_cap.h>
#include <bsd_auth.h>

auth_session_t *
auth_open(void);

int
auth_close(auth_session_t *as);

int
auth_call(auth_session_t *as, char *path, ...);

char *
auth_challenge(auth_session_t *as);

quad_t
auth_check_change(auth_session_t *as);

quad_t
auth_check_expire(auth_session_t *as);

void
auth_clean(auth_session_t *as);

void
auth_clrenv(auth_session_t *as);

void
auth_clroption(auth_session_t * as, char *name);

void
auth_clroptions(auth_session_t *as);

char *
auth_getitem(auth_session_t *as, auth_item_t item);

struct passwd *
auth_getpwd(auth_session_t *as);

int
auth_getstate(auth_session_t *as);

char *
auth_getvalue(auth_session_t *as, char *what);

void
auth_set_va_list(auth_session_t *as, va_list ap);

int
auth_setdata(auth_session_t *as, void *ptr, size_t len);

void
auth_setenv(auth_session_t *as);

int
auth_setitem(auth_session_t *as, auth_item_t item, char *value);

int
auth_setoption(auth_session_t *as, char *name, char *value);

int
auth_setpwd(auth_session_t *as, struct passwd *pwd);

void
auth_setstate(auth_session_t *as, int state);

These functions provide the lower level interface to the BSD Authentication system. They all operate on a BSD Authentication session pointer, as, which is returned by (). The session pointer must be passed to all other BSD Authentication functions called. The auth_open() function returns NULL if it was unable to allocate memory for the session. The session is terminated by the auth_close() function, which also sets any environment variables requested by the login script (assuming the user was not rejected) or removes files created by the login script if the authentication was not successful. It returns the final state of the authentication request. A return value of 0 implies the user was not authenticated. A non-zero return value is made up of 1 or more of the following values ORed together:

The user was authenticated.
The user was authenticated with a root instance.
The user was authenticated via a mechanism which is not subject to eavesdropping attacks (such as provided by token cards).

The full state of the session is returned by the () function. In addition to the values above, it also may contain the bits:

Do not report an error, the user was not authenticated for access and was not expected to be. This is returned by login scripts that allow changing of the user's password, for instance. This value is stripped off for normal returns.
The user was not authenticated for access and a challenge was issued. The challenge should be displayed to the user, a response retrieved, and the result verified. This value is stripped off for normal returns.
The user's account has expired.
The user's password has expired and needs to be changed.

A session may be cleaned by calling (). This function removes any files created by a login script in this session and clears all state associated with this session, with the exception of the option settings. It is not necessary to call auth_clean() if auth_close() is called.

The remaining functions are described in alphabetical order.

The fundamental function for doing BSD Authentication is (). In addition to the pointer to the BSD Authentication session, it takes the following parameters:

path
The full path name of the login script to run.
...
The remaining arguments, which should be of type char * and terminated with a NULL, are passed to the login script at the end of the command line. Non-optional arguments such as user should be prefixed by a "--" argument so that getopt(3) will not attempt to interpret them as optional flags.

The () function, after verifying the path, creates a bi-directional pipe (socketpair) which is located on file descriptor 3 for the child (the login script). This is known as the “back channel”. The actual command line passed to the child is made up of 3 parts. The parameters passed to auth_call() following path have appended to them any arguments specified by the auth_set_va_list() function. These are typically the variable arguments passed to the function that calls auth_call(). Any option values set by the auth_setoption() function are inserted between the first argument (the command name) and the second argument with a preceding -v flag. The name and value are separated by an ‘=’:

-v name=value

Once the login script has been spawned, any data specified by the () is written to the back channel. Multiple blocks of data may have been specified and they will be sent in the same order they were specified. As the data is sent, the storage for the data is zeroed out and then freed (the data is zeroed out since it may contain sensitive information, such as a password). Once any data is written out, auth_call() reads up to 8192 bytes of data from the back channel. The state of the session is determined from this data (see login.conf(5) for details). If the login script exits with a 0 and does not specify any return state on the back channel, the state prior to the call to auth_call() is retained.

Note that while () will zero out the copies it makes of sensitive information, such as plain text passwords, after it is sent, it is the responsibility of the caller to zero out the original copies of this sensitive information. Due to the mechanics of the auth_call() function, this data must be zeroed auth_call() is called. The safest place to zero out sensitive information is immediately after it has been passed to auth_setdata().

The back channel data may also contain a file descriptor passed back from the login script. If this is the case, the login script will first send back the string “fd” to indicate that a file descriptor will be the next data item. The file descriptor will be passed back to the next invocation of the login script with a number specified by the -v fd option. This is used to implement stateful challenge/response schemes that require a persistent connection during the challenge and response. The copy of the descriptor in the parent process is closed when the child is running to prevent deadlock when file locking is used. The descriptor is also closed by a call to () or auth_clean().

The data read from the back channel is also used by the () and auth_close() functions. Subsequent calls to auth_call() will cause this data to be lost and overwritten with the new data read from the new call.

The environment passed to the login script by () only contains two values: PATH and SHELL. The PATH is set to the default path (/bin and /usr/bin) while the SHELL is set to the default system shell (/bin/sh).

The () function queries the login script defined by the current style for a challenge for the user specified by name. (See below for the setting of the style and name). It internally uses the auth_call() function. The generated challenge is returned. NULL is returned on error or if no challenge was generated.

The () and () functions check the password expiration (change) and account expiration times. They return 0 if no change or expiration time is set for the account. They return a negative value of how many seconds have passed since the password or account expired. In this case the state of the session is marked with either AUTH_PWEXPIRED or AUTH_EXPIRED as well as clearing any bits which would indicate the authentication was successful. If the password or account has not expired, they return the number of seconds left until the account does expire. The return value of -1 can either indicate the password or account just expired or that no password entry was set for the current session.

The () function clears any requests set by a login script for environment variables to be set.

The () function clears the previously set option name.

The () function clears all previously set options.

The () function returns the value of item. The item may be one of:

The latest challenge, if any, set for the session.
The class of the user, as defined by the /etc/login.conf file. This value is not directly used by BSD Authentication, rather, it is passed to the login scripts for their possible use.
If set to any value, then the session is tagged as interactive. If not set, the session is not interactive. When the value is requested, it is always either NULL or “True”. The auth subroutines may choose to provide additional information to standard output or standard error when the session is interactive. There is no functional change in the operation of the subroutines.
The name of the user being authenticated. The name should include the instance, if any, that is being requested.
The service requesting the authentication. Initially it is set to the default service which provides the traditional interactive service.
The style of authentication being performed, as defined by the /etc/login.conf file. The style determines which login script should actually be used.

The value returned points to private memory and should not be freed by the caller.

The () function returns the value, if any, associated with the specified internal variable what. These variables are set by login scripts. When a new login script is run (by the auth_call() function), the values from the previous login script are lost. (See login.conf(5) for details on internal variables.)

The () function establishes a variable argument list to be used by the auth_call() function. It is intended to be used by functions which need to call auth_call() but take a variable number of arguments themselves. Since the arguments are not copied, the call to auth_call() must be placed within the scope of ap. The auth_call() function will call va_end(3) on ap.

The () function makes a copy of len bytes of data pointed to by ptr for use by auth_call(). The data will be passed on the back channel to the next login script called.

The () function adds/deletes any environment variables requested by the login script to the current environment.

The () function assigns value to the specified item. The items are described above with the auth_getitem() function. In addition, if value is NULL, the item is cleared. If value is NULL and item is AUTH_ALL then all items are cleared.

The () function requests that the option name be set with the value of value when a script is executed by auth_call(). The actual arguments to the script will be placed at the beginning of the argument vector. For each option two arguments will be issued: -v name=value.

The function () establishes the password file entry for the authentication session. If the name has already been set by auth_setitem() then the pwd argument may be NULL, else it must be the password entry to use.

The function () retrieves the saved password file entry for the authentication session. If no entry has been saved (either explicitly via auth_setpwd() or implicitly via auth_check_expire() or auth_check_change()), it returns NULL. Note that the memory containing the password file entry is freed by a call to auth_close() or auth_clean().

The function () sets the sessions state to state. Typically this is either AUTH_OKAY or 0.

authenticate(3), login_cap(3), pw_dup(3), login.conf(5)

February 19, 2023 OpenBSD-current