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SSL_CTX_set_cert_verify_callback - set peer certificate verification
void SSL_CTX_set_cert_verify_callback(SSL_CTX *ctx,
int (*callback)(X509_STORE_CTX *, void *),
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