NAME

       SSL_CTX_use_psk_identity_hint, SSL_use_psk_identity_hint, SSL_CTX_set_psk_server_callback,
       SSL_set_psk_server_callback - set PSK identity hint to use

SYNOPSIS

        #include <openssl/ssl.h>

        int SSL_CTX_use_psk_identity_hint(SSL_CTX *ctx, const char *hint);
        int SSL_use_psk_identity_hint(SSL *ssl, const char *hint);

        void SSL_CTX_set_psk_server_callback(SSL_CTX *ctx,
               unsigned int (*callback)(SSL *ssl, const char *identity,
               unsigned char *psk, int max_psk_len));
        void SSL_set_psk_server_callback(SSL *ssl,
               unsigned int (*callback)(SSL *ssl, const char *identity,
               unsigned char *psk, int max_psk_len));

DESCRIPTION

       SSL_CTX_use_psk_identity_hint() sets the given NULL-terminated PSK identity hint hint to
       SSL context object ctx. SSL_use_psk_identity_hint() sets the given NULL-terminated PSK
       identity hint hint to SSL connection object ssl. If hint is NULL the current hint from ctx
       or ssl is deleted.

       In the case where PSK identity hint is NULL, the server does not send the
       ServerKeyExchange message to the client.

       A server application must provide a callback function which is called when the server
       receives the ClientKeyExchange message from the client. The purpose of the callback
       function is to validate the received PSK identity and to fetch the pre-shared key used
       during the connection setup phase. The callback is set using functions
       SSL_CTX_set_psk_server_callback() or SSL_set_psk_server_callback(). The callback function
       is given the connection in parameter ssl, NULL-terminated PSK identity sent by the client
       in parameter identity, and a buffer psk of length max_psk_len bytes where the pre-shared
       key is to be stored.

RETURN VALUES

       SSL_CTX_use_psk_identity_hint() and SSL_use_psk_identity_hint() return 1 on success, 0
       otherwise.

       Return values from the server callback are interpreted as follows:

       > 0 PSK identity was found and the server callback has provided the PSK successfully in
           parameter psk. Return value is the length of psk in bytes. It is an error to return a
           value greater than max_psk_len.

           If the PSK identity was not found but the callback instructs the protocol to continue
           anyway, the callback must provide some random data to psk and return the length of the
           random data, so the connection will fail with decryption_error before it will be
           finished completely.

       0   PSK identity was not found. An "unknown_psk_identity" alert message will be sent and
           the connection setup fails.