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- =pod
- =head1 NAME
- SSL_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 DESCRIPTION
- SSL_CTX_set_cert_verify_callback() sets the verification callback function for
- I<ctx>. SSL objects that are created from I<ctx> inherit the setting valid at
- the time when L<SSL_new(3)|SSL_new(3)> is called.
- =head1 NOTES
- 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 I<callback> is specified via
- SSL_CTX_set_cert_verify_callback(), the supplied callback function is called
- instead. By setting I<callback> to NULL, the default behaviour is restored.
- When the verification must be performed, I<callback> will be called with
- the 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 to
- indicate verification failure. If SSL_VERIFY_PEER is set and I<callback>
- returns 0, the handshake will fail. As the verification procedure may
- allow 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 informed
- about 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 WARNINGS
- Do not mix the verification callback described in this function with the
- B<verify_callback> function called during the verification process. The
- latter 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 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 B<verify_callback> function.
- =head1 BUGS
- =head1 RETURN VALUES
- SSL_CTX_set_cert_verify_callback() does not provide diagnostic information.
- =head1 SEE ALSO
- L<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 HISTORY
- Previous 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 dummy
- argument will have to be added to I<callback>.
- =cut
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