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SSL_CTX_set_cert_verify_callback(3)                                    OpenSSL

       SSL_CTX_set_cert_verify_callback - set peer certificate verification

       libcrypto, -lcrypto

        #include <openssl/ssl.h>

        void SSL_CTX_set_cert_verify_callback(SSL_CTX *ctx,
                                              int (*callback)(X509_STORE_CTX *, void *),
                                              void *arg);

       SSL_CTX_set_cert_verify_callback() sets the verification callback
       function for ctx. SSL objects that are created from ctx inherit the
       setting valid at the time when SSL_new(3) is called.

       Whenever a certificate is verified during a SSL/TLS handshake, a
       verification function is called. If the application does not explicitly
       specify a verification callback function, the built-in verification
       function is used.  If a verification callback callback is specified via
       SSL_CTX_set_cert_verify_callback(), the supplied callback function is
       called instead. By setting callback to NULL, the default behaviour is

       When the verification must be performed, callback will be called with
       the arguments callback(X509_STORE_CTX *x509_store_ctx, void *arg). The
       argument arg is specified by the application when setting callback.

       callback should return 1 to indicate verification success and 0 to
       indicate verification failure. If SSL_VERIFY_PEER is set and callback
       returns 0, the handshake will fail. As the verification procedure may
       allow the connection to continue in the case of failure (by always
       returning 1) the verification result must be set in any case using the
       error member of x509_store_ctx so that the calling application will be
       informed about the detailed result of the verification procedure!

       Within x509_store_ctx, callback has access to the verify_callback
       function set using SSL_CTX_set_verify(3).

       SSL_CTX_set_cert_verify_callback() does not return a value.

       Do not mix the verification callback described in this function with
       the verify_callback function called during the verification process.
       The latter is set using the SSL_CTX_set_verify(3) family of functions.

       Providing a complete verification procedure including certificate
       purpose settings etc is a complex task. The built-in procedure is quite
       powerful and in most cases it should be sufficient to modify its
       behaviour using the verify_callback function.

       SSL_CTX_set_cert_verify_callback() does not provide diagnostic

       ssl(7), SSL_CTX_set_verify(3), SSL_get_verify_result(3),

       Copyright 2001-2018 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

1.1.1i                            2018-09-23