Initial Commit

openssl-1.0.2f/doc/ssl/SSL_CTX_set_cert_verify_callback.pod

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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