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.\" ========================================================================
.\"
.IX Title "SSL_CTX_set_psk_client_callback 3"
.TH SSL_CTX_set_psk_client_callback 3 "2019-12-20" "1.0.2u" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.nh
.SH "NAME"
SSL_CTX_set_psk_client_callback, SSL_set_psk_client_callback \- set PSK client callback
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #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));
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
A client application must provide a callback function which is called
when the client is sending the ClientKeyExchange message to the server.
.PP
The purpose of the callback function is to select the \s-1PSK\s0 identity and
the pre-shared key to use during the connection setup phase.
.PP
The callback is set using functions \fBSSL_CTX_set_psk_client_callback()\fR
or \fBSSL_set_psk_client_callback()\fR. The callback function is given the
connection in parameter \fBssl\fR, a \fB\s-1NULL\s0\fR\-terminated \s-1PSK\s0 identity hint
sent by the server in parameter \fBhint\fR, a buffer \fBidentity\fR of
length \fBmax_identity_len\fR bytes where the the resulting
\&\fB\s-1NULL\s0\fR\-terminated identity is to be stored, and a buffer \fBpsk\fR of
length \fBmax_psk_len\fR bytes where the resulting pre-shared key is to
be stored.
.SH "NOTES"
.IX Header "NOTES"
Note that parameter \fBhint\fR given to the callback may be \fB\s-1NULL\s0\fR.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
Return values from the client callback are interpreted as follows:
.PP
On success (callback found a \s-1PSK\s0 identity and a pre-shared key to use)
the length (> 0) of \fBpsk\fR in bytes is returned.
.PP
Otherwise or on errors callback should return 0. In this case
the connection setup fails.