=pod=head1 NAMESSL_CTX_set_cert_verify_callback - set peer certificate verification procedure=head1 SYNOPSIS #include <openssl/ssl.h> void SSL_CTX_set_cert_verify_callback(SSL_CTX *ctx, int (*callback)(X509_STORE_CTX *,void *), void *arg);=head1 DESCRIPTIONSSL_CTX_set_cert_verify_callback() sets the verification callback function forI<ctx>. SSL objects that are created from I<ctx> inherit the setting valid atthe time when L<SSL_new(3)|SSL_new(3)> is called.=head1 NOTESWhenever a certificate is verified during a SSL/TLS handshake, a verificationfunction is called. If the application does not explicitly specify averification callback function, the built-in verification function is used.If a verification callback I<callback> is specified viaSSL_CTX_set_cert_verify_callback(), the supplied callback function is calledinstead. By setting I<callback> to NULL, the default behaviour is restored.When the verification must be performed, I<callback> will be called withthe arguments callback(X509_STORE_CTX *x509_store_ctx, void *arg). The argument I<arg> is specified by the application when setting I<callback>.I<callback> should return 1 to indicate verification success and 0 toindicate verification failure. If SSL_VERIFY_PEER is set and I<callback>returns 0, the handshake will fail. As the verification procedure mayallow to continue the connection in case of failure (by always returning 1)the verification result must be set in any case using the B<error>member of I<x509_store_ctx> so that the calling application will be informedabout the detailed result of the verification procedure! Within I<x509_store_ctx>, I<callback> has access to the I<verify_callback>function set using L<SSL_CTX_set_verify(3)|SSL_CTX_set_verify(3)>.=head1 WARNINGSDo not mix the verification callback described in this function with theB<verify_callback> function called during the verification process. Thelatter is set using the L<SSL_CTX_set_verify(3)|SSL_CTX_set_verify(3)>family of functions.Providing a complete verification procedure including certificate purposesettings etc is a complex task. The built-in procedure is quite powerfuland in most cases it should be sufficient to modify its behaviour usingthe B<verify_callback> function.=head1 BUGS=head1 RETURN VALUESSSL_CTX_set_cert_verify_callback() does not provide diagnostic information.=head1 SEE ALSOL<ssl(3)|ssl(3)>, L<SSL_CTX_set_verify(3)|SSL_CTX_set_verify(3)>,L<SSL_get_verify_result(3)|SSL_get_verify_result(3)>,L<SSL_CTX_load_verify_locations(3)|SSL_CTX_load_verify_locations(3)>=head1 HISTORYPrevious to OpenSSL 0.9.7, the I<arg> argument to B<SSL_CTX_set_cert_verify_callback>was ignored, and I<callback> was called simply as int (*callback)(X509_STORE_CTX *)To compile software written for previous versions of OpenSSL, a dummyargument will have to be added to I<callback>.=cut