void SSL_CTX_set_cert_verify_callback(SSL_CTX *ctx, int (*callback)(X509_STORE_CTX *,void *), void *arg);
DESCRIPTION
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.
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 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 restored.
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 to continue the connection in 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).
WARNINGS
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.
BUGS
RETURN VALUES
SSL_CTX_set_cert_verify_callback() does not provide diagnostic information.
Previous to OpenSSL 0.9.7, the arg argument to SSL_CTX_set_cert_verify_callback
was ignored, and 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 callback.
