1SSL_CTX_set_cert_verify_callback(3) OpenSSLSSL_CTX_set_cert_verify_callback(3)
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NAME

6       SSL_CTX_set_cert_verify_callback - set peer certificate verification
7       procedure
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SYNOPSIS

10        #include <openssl/ssl.h>
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12        void SSL_CTX_set_cert_verify_callback(SSL_CTX *ctx, int (*callback)(X509_STORE_CTX *,void *), void *arg);
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DESCRIPTION

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

20       Whenever a certificate is verified during a SSL/TLS handshake, a
21       verification function is called. If the application does not explicitly
22       specify a verification callback function, the built-in verification
23       function is used.  If a verification callback callback is specified via
24       SSL_CTX_set_cert_verify_callback(), the supplied callback function is
25       called instead. By setting callback to NULL, the default behaviour is
26       restored.
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28       When the verification must be performed, callback will be called with
29       the arguments callback(X509_STORE_CTX *x509_store_ctx, void *arg). The
30       argument arg is specified by the application when setting callback.
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32       callback should return 1 to indicate verification success and 0 to
33       indicate verification failure. If SSL_VERIFY_PEER is set and callback
34       returns 0, the handshake will fail. As the verification procedure may
35       allow to continue the connection in case of failure (by always
36       returning 1) the verification result must be set in any case using the
37       error member of x509_store_ctx so that the calling application will be
38       informed about the detailed result of the verification procedure!
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40       Within x509_store_ctx, callback has access to the verify_callback
41       function set using SSL_CTX_set_verify(3).
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WARNINGS

44       Do not mix the verification callback described in this function with
45       the verify_callback function called during the verification process.
46       The latter is set using the SSL_CTX_set_verify(3) family of functions.
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48       Providing a complete verification procedure including certificate
49       purpose settings etc is a complex task. The built-in procedure is quite
50       powerful and in most cases it should be sufficient to modify its
51       behaviour using the verify_callback function.
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BUGS

RETURN VALUES

55       SSL_CTX_set_cert_verify_callback() does not provide diagnostic
56       information.
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SEE ALSO

59       ssl(3), SSL_CTX_set_verify(3), SSL_get_verify_result(3),
60       SSL_CTX_load_verify_locations(3)
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HISTORY

63       Previous to OpenSSL 0.9.7, the arg argument to
64       SSL_CTX_set_cert_verify_callback was ignored, and callback was called
65       simply as
66        int (*callback)(X509_STORE_CTX *) To compile software written for
67       previous versions of OpenSSL, a dummy argument will have to be added to
68       callback.
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721.0.2o                            2020-01-28SSL_CTX_set_cert_verify_callback(3)