=pod

=begin comment

Copyright 2005 Nokia. All rights reserved.

The portions of the attached software ("Contribution") is developed by
Nokia Corporation and is licensed pursuant to the OpenSSL open source
license.

The Contribution, originally written by Mika Kousa and Pasi Eronen of
Nokia Corporation, consists of the "PSK" (Pre-Shared Key) ciphersuites
support (see RFC 4279) to OpenSSL.

No patent licenses or other rights except those expressly stated in
the OpenSSL open source license shall be deemed granted or received
expressly, by implication, estoppel, or otherwise.

No assurances are provided by Nokia that the Contribution does not
infringe the patent or other intellectual property rights of any third
party or that the license provides you with all the necessary rights
to make use of the Contribution.

THE SOFTWARE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. IN
ADDITION TO THE DISCLAIMERS INCLUDED IN THE LICENSE, NOKIA
SPECIFICALLY DISCLAIMS ANY LIABILITY FOR CLAIMS BROUGHT BY YOU OR ANY
OTHER ENTITY BASED ON INFRINGEMENT OF INTELLECTUAL PROPERTY RIGHTS OR
OTHERWISE.

=end comment

=head1 NAME

SSL_CTX_set_psk_client_callback, SSL_set_psk_client_callback - set PSK client callback

=head1 SYNOPSIS

 #include <openssl/ssl.h>

 void SSL_CTX_set_psk_client_callback(SSL_CTX *ctx,
	unsigned int (*callback)(SSL *ssl, const char *hint,
	char *identity, unsigned int max_identity_len,
	unsigned char *psk, unsigned int max_psk_len));
 void SSL_set_psk_client_callback(SSL *ssl,
	unsigned int (*callback)(SSL *ssl, const char *hint,
	char *identity, unsigned int max_identity_len,
 	unsigned char *psk, unsigned int max_psk_len));


=head1 DESCRIPTION

A client application must provide a callback function which is called
when the client is sending the ClientKeyExchange message to the server.

The purpose of the callback function is to select the PSK identity and
the pre-shared key to use during the connection setup phase.

The callback is set using functions SSL_CTX_set_psk_client_callback()
or SSL_set_psk_client_callback(). The callback function is given the
connection in parameter B<ssl>, a B<NULL>-terminated PSK identity hint
sent by the server in parameter B<hint>, a buffer B<identity> of
length B<max_identity_len> bytes where the the resulting
B<NULL>-terminated identity is to be stored, and a buffer B<psk> of
length B<max_psk_len> bytes where the resulting pre-shared key is to
be stored.

=head1 NOTES

Note that parameter B<hint> given to the callback may be B<NULL>.

=head1 RETURN VALUES

Return values from the client callback are interpreted as follows:

On success (callback found a PSK identity and a pre-shared key to use)
the length (> 0) of B<psk> in bytes is returned.

Otherwise or on errors callback should return 0. In this case
the connection setup fails.

=cut