SASL client library - draft
---------------------------

Version: $NetBSD: library.txt,v 1.3 2011/02/11 23:44:42 christos Exp $

1. Typedefs

Moved to src/*.h

2. Public API

saslc_t *saslc_init(const char *appname); - Function takes appname as an
argument, function allocates and initializes new saslc_t structure, parses
configuration files if available (/etc/saslc/appname.d/sasl.conf and then
/etc/saslc/appname.d/mechanism.conf for machanisms which are listed in 
sasl.conf) Function returns pointer to the saslc_t on success and NULL on
failure.

const char *saslc_strerror(saslc_t *saslc); - function maps last error
number in saslc to the message string. Returns pointer to the message string
on success and pointer to the "unknown error" string on failure.

int saslc_end(saslc_t *saslc); - function destroys SASL library context and
deallocates any resources used. If any sessions are assigned to the context
then function closes them. It returns 0 on success and -1 on failure.

saslc_sess_t *saslc_sess_init(saslc_t *saslc, const char *mechs); - Function
creates a new sasl session. If saslc is NULL then default configuration
settings are used. Mechs is the string which consists of a comma separated
list of mechanism names. Mechanism used for the authentication is selected
basing on the configuration. Function allocates saslc_sess_t and performs
initialization of saslc_sess_t, pointer to it is returned on success and NULL
is returned on failure. In case of a failure saslc errno is set.

int saslc_sess_setprop(saslc_sess_t *sess, const char *name,
    const char *value); - Functions sets a property in the session. This
function is used for setting i.e. callbacks.  It returns 0 on success and -1
on failure. In case of a failure sess errno is set.

NOTE: Property is added to the sess->prop dictionary.
NOTE: All properties' names should match to [A-Za-z0-9_]+.

const char  *saslc_sess_getprop(saslc_sess_t *sess, const char *name); -
Function gets property from the session. It return pointer to the property
value on success and NULL on failure. In case of a failure sess errno is
set.

NOTE: Property is taken from the sess->prop dictionary, if property not exist
then sess->context->prop is used with added sess->mech->name."-" prefix.

int saslc_sess_cont(saslc_sess_t *sess, const char *in, size_t inlen, 
    char **out, size_t *outlen); - Function performs one step of the SASL
authentication. Input data of length inlen is passed in the "in" argument.
Function stores output of length outlen in the out argument and returns 0 on
success, 1 if more steps of the SASL authentication is needed and -1 on
failure. In case of a failure sess errno is set.

NOTE: user is responsible for deallocate the output data.
IMPLEMENTATION: sess->mech->cont(sess, in, inlen, out, outlen)

const char *saslc_sess_strerror(saslc_sess_t *sess); - function maps last 
error number in sess to message string. Returns pointer to the message string
on success and pointer to the "unknown error" string on failure.

const char *saslc_sess_strmech(saslc_sess_t *sess); - function returns pointer 
to the string contains name of the mechanism used in session. On failure
function returns pointer to "unknown".

int saslc_sess_encode(saslc_sess_t *sess, const char *in, size_t inlen,
    char **out, size_t *outlen); - function encodes data using security layer
negotiated during the authentication. Returns 0 on success, -1 on failure. In
case of a failure sess errno is set.
IMPLEMENTATION: sess->mech->encode(sess, in, inlen, out, outlen)

int saslc_sess_decode(saslc_sess_t *sess, const char *in, size_t inlen,
    char **out, size_t *outlen); - function decodes data using security layer
negotiated during the authentication. Returns 0 on success, -1 on failure. In
case of a failure sess errno is set.
IMPLEMENTATION: sess->mech->decode(sess, in, inlen, out, outlen)

void saslc_sess_end(saslc_sess_t *sess); - function destroys SASL session and
deallocates any resources used.

3. Mechanisms

3.1. Global mechanisms table

saslc_mech_list_t *mechanisms;

List of mechanisms, initialized during first call of saslc_start(...);

3.3. Mechanisms implementation

Each mechanism will provide const saslc_mech_t structure describing its
implementation. Mechanisms state is described by saslc_mech_sess_t, using this
type by mechanism is not mandatory and different struct can be defined by a
mechanism if necessary. This structure is used only for representing internal
state of the mechanism session, and wouldn't be used outside of mechanism
implementation.

3.2. Mechanisms which are going to be implemented

 * ANONYMOUS (create, destroy, cont)
 * EXTERNAL (create, destroy, cont)
 * PLAIN (create, destroy, cont)
 * LOGIN (create, destroy, cont)
 * CRAM-MD5 (create, destroy, cont)
 * DIGEST-MD5 (create, destroy, cont, encode, decode)
 * GSSAPI (create, destroy, cont, encode, decode)

3.3. Example

 Consider ANONYMOUS mechanism as example, its pseudo implementation looks as
follows:

generic_create(...) {
        // create mech_sess structure
        // mech_sess->status = AUTHENTICATION
}

anon_cont(...) {
        char *token;

        if ( mech_sess->status != AUTHENTICATION ) {
                // error handler
        }

        // get token from session if present, if not use default from
        // configuration

        // output = token, outlen = lenght(token)
        // mech_sess->status = AUTHENTICATED...
        // return 0;
}

generic_destroy(...) {
        // destroy mech_sess structure
        // return
}

saslc_mech_t anon_mech = {
        "ANONYMOUS", // const char *name;
        FLAG_ANONYMOUS, /* mechanism flags */
        mech_generic_create; /* create function - creates mechanism 
                                instance */
        mech_anonymous_cont; /* step function - performs one step of 
                                authentication */
        NULL; /* encoding function - encodes input
                 according to negotiated security layer */
        NULL; /* decoding function - decodes input
                 according to negotiated security layer */
        mech_generic_destroy; /* destroy function - destroys mechanism
                            instance */
} mech_anonymous;


4. Expected usage

Below is presented example and expected usage of the library.

/* creating context */
...
ctx = saslc_init("example");

if ( ctx == NULL ) {
        //error handler
}
...


/* session */
sess = saslc_sess_init(ctx, "PLAIN,ANONYMOUS");

if ( sess == NULL ) {
        //error handler
}

if ( strcmp(saslc_sess_strmech(sess),"PLAIN") == 0 ) {
        saslc_sess_setprop(sess, "USERID", "foo");
        saslc_sess_setprop(sess, "PASSWORD", "bar");
} else if ( strcmp(saslc_sess_strmech(sess),"ANONYMOUS") == 0 ) {
        saslc_sess_setprop(sess, "TOKEN", "foo@bar.com");
}

// sending auth
// proto read
// parse

while ( (last = sasl_sess_cont(sess, in, inlen, out, outlen)) >= 0 ) {
        // proto send
        // proto read
        // parse

        if ( last == 0 )
                break;
}

if ( last == 0 ) {
        // yay!
} else {
        // error handler
}

...
/* destroying session and context */
saslc_sess_end(sess);
saslc_end(ctx);
...

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