SSL_CTX_set_stateless_cookie_generate_cb, SSL_CTX_set_stateless_cookie_verify_cb,

       Copyright 2018 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the Apache License 2.0 (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
       <https://www.openssl.org/source/license.html>.

3.5.0                                              2025-06-04     SSL_CTX_SET_STATELESS_COOKIE_GENERATE_CB(3SSL)

SSL_CTX_set_stateless_cookie_generate_cb() sets the callback used by SSL_stateless(3) to generate the
       application-controlled portion of the cookie provided to clients in the HelloRetryRequest transmitted as
       a response to a ClientHello with a missing or invalid cookie. gen_stateless_cookie_cb() must write at
       most SSL_COOKIE_LENGTH bytes into cookie, and must write the number of bytes written to cookie_len. If a
       cookie cannot be generated, a zero return value can be used to abort the handshake.

       SSL_CTX_set_stateless_cookie_verify_cb() sets the callback used by SSL_stateless(3) to determine whether
       the application-controlled portion of a ClientHello cookie is valid. The cookie data is pointed to by
       cookie and is of length cookie_len. A nonzero return value from verify_stateless_cookie_cb() communicates
       that the cookie is valid. The integrity of the entire cookie, including the application-controlled
       portion, is automatically verified by HMAC before verify_stateless_cookie_cb() is called.

       SSL_CTX_set_cookie_generate_cb() sets the callback used by DTLSv1_listen(3) to generate the cookie
       provided to clients in the HelloVerifyRequest transmitted as a response to a ClientHello with a missing
       or invalid cookie.  app_gen_cookie_cb()  must write at most DTLS1_COOKIE_LENGTH bytes into cookie, and
       must write the number of bytes written to cookie_len. If a cookie cannot be generated, a zero return
       value can be used to abort the handshake.

       SSL_CTX_set_cookie_verify_cb() sets the callback used by DTLSv1_listen(3) to determine whether the cookie
       in a ClientHello is valid. The cookie data is pointed to by cookie and is of length cookie_len. A nonzero
       return value from app_verify_cookie_cb() communicates that the cookie is valid. The integrity of the
       cookie is not verified by OpenSSL. This is an application responsibility.

SSL_CTX_set_stateless_cookie_generate_cb() and SSL_CTX_set_stateless_cookie_verify_cb() were added in
       OpenSSL 1.1.1.

       SSL_CTX_set_stateless_cookie_generate_cb, SSL_CTX_set_stateless_cookie_verify_cb,
       SSL_CTX_set_cookie_generate_cb, SSL_CTX_set_cookie_verify_cb - Callback functions for stateless TLS1.3
       cookies

       Neither function returns a value.

ssl(7), SSL_stateless(3), DTLSv1_listen(3)

        #include <openssl/ssl.h>

        void SSL_CTX_set_stateless_cookie_generate_cb(
            SSL_CTX *ctx,
            int (*gen_stateless_cookie_cb) (SSL *ssl,
                                            unsigned char *cookie,
                                            size_t *cookie_len));
        void SSL_CTX_set_stateless_cookie_verify_cb(
            SSL_CTX *ctx,
            int (*verify_stateless_cookie_cb) (SSL *ssl,
                                               const unsigned char *cookie,
                                               size_t cookie_len));

        void SSL_CTX_set_cookie_generate_cb(SSL_CTX *ctx,
                                            int (*app_gen_cookie_cb) (SSL *ssl,
                                                                      unsigned char
                                                                      *cookie,
                                                                      unsigned int
                                                                      *cookie_len));
        void SSL_CTX_set_cookie_verify_cb(SSL_CTX *ctx,
                                          int (*app_verify_cookie_cb) (SSL *ssl,
                                                                       const unsigned
                                                                       char *cookie,
                                                                       unsigned int
                                                                       cookie_len));