5 SSL_CTX_set_cert_verify_callback - set peer certificate verification procedure
9 #include <openssl/ssl.h>
11 void SSL_CTX_set_cert_verify_callback(SSL_CTX *ctx,
12 int (*callback)(X509_STORE_CTX *, void *),
17 SSL_CTX_set_cert_verify_callback() sets the verification callback function for
18 I<ctx>. SSL objects that are created from I<ctx> inherit the setting valid at
19 the time when L<SSL_new(3)> is called.
23 Whenever a certificate is verified during a SSL/TLS handshake, a verification
24 function is called. If the application does not explicitly specify a
25 verification callback function, the built-in verification function is used.
26 If a verification callback I<callback> is specified via
27 SSL_CTX_set_cert_verify_callback(), the supplied callback function is called
28 instead. By setting I<callback> to NULL, the default behaviour is restored.
30 When the verification must be performed, I<callback> will be called with
31 the arguments callback(X509_STORE_CTX *x509_store_ctx, void *arg). The
32 argument I<arg> is specified by the application when setting I<callback>.
34 I<callback> should return 1 to indicate verification success and 0 to
35 indicate verification failure. If SSL_VERIFY_PEER is set and I<callback>
36 returns 0, the handshake will fail.
38 In client mode I<callback> may also return -1,
39 typically on failure verifying the server certificate.
40 This makes the handshake suspend and return control to the calling application
41 with B<SSL_ERROR_WANT_RETRY_VERIFY>.
42 The app can for instance fetch further certificates or cert status information
43 needed for the verification.
44 Calling L<SSL_connect(3)> again resumes the connection attempt
45 by retrying the server certificate verification step.
46 This process may even be repeated if need be.
48 As the verification procedure may
49 allow the connection to continue in the case of failure (by always
50 returning 1) the verification result must be set in any case using the
51 B<error> member of I<x509_store_ctx> so that the calling application
52 will be informed about the detailed result of the verification procedure!
54 Within I<x509_store_ctx>, I<callback> has access to the I<verify_callback>
55 function set using L<SSL_CTX_set_verify(3)>.
59 SSL_CTX_set_cert_verify_callback() does not return a value.
63 Do not mix the verification callback described in this function with the
64 B<verify_callback> function called during the verification process. The
65 latter is set using the L<SSL_CTX_set_verify(3)>
68 Providing a complete verification procedure including certificate purpose
69 settings etc is a complex task. The built-in procedure is quite powerful
70 and in most cases it should be sufficient to modify its behaviour using
71 the B<verify_callback> function.
75 SSL_CTX_set_cert_verify_callback() does not provide diagnostic information.
79 L<ssl(7)>, L<SSL_CTX_set_verify(3)>,
80 L<SSL_get_verify_result(3)>,
81 L<SSL_CTX_load_verify_locations(3)>
85 Copyright 2001-2021 The OpenSSL Project Authors. All Rights Reserved.
87 Licensed under the Apache License 2.0 (the "License"). You may not use
88 this file except in compliance with the License. You can obtain a copy
89 in the file LICENSE in the source distribution or at
90 L<https://www.openssl.org/source/license.html>.