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SSL_CTX_set_tlsext_servername_callback(3)                              OpenSSL

       SSL_CTX_set_tlsext_servername_arg, SSL_get_servername_type,
       SSL_get_servername, SSL_set_tlsext_host_name - handle server name
       indication (SNI)

       libcrypto, -lcrypto

        #include <openssl/ssl.h>

        long SSL_CTX_set_tlsext_servername_callback(SSL_CTX *ctx,
                                          int (*cb)(SSL *, int *, void *));
        long SSL_CTX_set_tlsext_servername_arg(SSL_CTX *ctx, void *arg);

        const char *SSL_get_servername(const SSL *s, const int type);
        int SSL_get_servername_type(const SSL *s);

        int SSL_set_tlsext_host_name(const SSL *s, const char *name);

       The functionality provided by the servername callback is superseded by
       the ClientHello callback, which can be set using
       SSL_CTX_set_client_hello_cb().  The servername callback is retained for
       historical compatibility.

       SSL_CTX_set_tlsext_servername_callback() sets the application callback
       cb used by a server to perform any actions or configuration required
       based on the servername extension received in the incoming connection.
       When cb is NULL, SNI is not used. The arg value is a pointer which is
       passed to the application callback.

       SSL_CTX_set_tlsext_servername_arg() sets a context-specific argument to
       be passed into the callback for this SSL_CTX.

       SSL_get_servername() returns a servername extension value of the
       specified type if provided in the Client Hello or NULL.

       SSL_get_servername_type() returns the servername type or -1 if no
       servername is present. Currently the only supported type (defined in
       RFC3546) is TLSEXT_NAMETYPE_host_name.

       SSL_set_tlsext_host_name() sets the server name indication ClientHello
       extension to contain the value name. The type of server name indication
       extension is set to TLSEXT_NAMETYPE_host_name (defined in RFC3546).

       Several callbacks are executed during ClientHello processing, including
       the ClientHello, ALPN, and servername callbacks.  The ClientHello
       callback is executed first, then the servername callback, followed by
       the ALPN callback.

       The SSL_set_tlsext_host_name() function should only be called on SSL
       objects that will act as clients; otherwise the configured name will be

       SSL_CTX_set_tlsext_servername_callback() and
       SSL_CTX_set_tlsext_servername_arg() both always return 1 indicating
       success.  SSL_set_tlsext_host_name() returns 1 on success, 0 in case of

       ssl(7), SSL_CTX_set_alpn_select_cb(3), SSL_get0_alpn_selected(3),

       Copyright 2017 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the OpenSSL license (the "License").  You may not use
       this file except in compliance with the License.  You can obtain a copy
       in the file LICENSE in the source distribution or at

1.1.1                             2018-09-17