SSL_CTX_set_cert_verify_callback.pod revision 89837 
1=pod
2
3=head1 NAME
4
5SSL_CTX_set_cert_verify_callback - set peer certificate verification procedure
6
7=head1 SYNOPSIS
8
9 #include <openssl/ssl.h>
10
11 void SSL_CTX_set_cert_verify_callback(SSL_CTX *ctx, int (*callback)(),
12                                       char *arg);
13 int (*callback)();
14
15=head1 DESCRIPTION
16
17SSL_CTX_set_cert_verify_callback() sets the verification callback function for
18B<ctx>. SSL objects, that are created from B<ctx> inherit the setting valid at
19the time, L<SSL_new(3)|SSL_new(3)> is called. B<arg> is currently ignored.
20
21=head1 NOTES
22
23Whenever a certificate is verified during a SSL/TLS handshake, a verification
24function is called. If the application does not explicitly specify a
25verification callback function, the built-in verification function is used.
26If a verification callback B<callback> is specified via
27SSL_CTX_set_cert_verify_callback(), the supplied callback function is called
28instead. By setting B<callback> to NULL, the default behaviour is restored.
29
30When the verification must be performed, B<callback> will be called with
31the argument callback(X509_STORE_CTX *x509_store_ctx). The arguments B<arg>
32that can be specified when setting B<callback> are currently ignored.
33
34B<callback> should return 1 to indicate verification success and 0 to
35indicate verification failure. If SSL_VERIFY_PEER is set and B<callback>
36returns 0, the handshake will fail. As the verification procedure may
37allow to continue the connection in case of failure (by always returning 1)
38the verification result must be set in any case using the B<error>
39member of B<x509_store_ctx>, so that the calling application will be informed
40about the detailed result of the verification procedure! 
41
42Within B<x509_store_ctx>, B<callback> has access to the B<verify_callback>
43function set using L<SSL_CTX_set_verify(3)|SSL_CTX_set_verify(3)>.
44
45=head1 WARNINGS
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47Do not mix the verification callback described in this function with the
48B<verify_callback> function called during the verification process. The
49latter is set using the L<SSL_CTX_set_verify(3)|SSL_CTX_set_verify(3)>
50family of functions.
51
52Providing a complete verification procedure including certificate purpose
53settings etc is a complex task. The built-in procedure is quite powerful
54and in most cases it should be sufficient to modify its behaviour using
55the B<verify_callback> function.
56
57=head1 BUGS
58
59It is possible to specify arguments to be passed to the verification callback.
60Currently they are however not passed but ignored.
61
62The B<callback> function is not specified via a prototype, so that no
63type checking takes place.
64
65=head1 RETURN VALUES
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67SSL_CTX_set_cert_verify_callback() does not provide diagnostic information.
68
69=head1 SEE ALSO
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71L<ssl(3)|ssl(3)>, L<SSL_CTX_set_verify(3)|SSL_CTX_set_verify(3)>,
72L<SSL_get_verify_result(3)|SSL_get_verify_result(3)>,
73L<SSL_CTX_load_verify_locations(3)|SSL_CTX_load_verify_locations(3)>
74
75=cut
76