_find_session_callback(SSL *s, SSL_psk_find_session_cb_func cb);

 typedef unsigned int (*SSL_psk_server_cb_func)(SSL *ssl,
                                                const char *identity,
                                                unsigned char *psk,
                                                unsigned int max_psk_len);

 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