1SSL_CTX_set_cert_cb(3)              OpenSSL             SSL_CTX_set_cert_cb(3)
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NAME

6       SSL_CTX_set_cert_cb, SSL_set_cert_cb - handle certificate callback
7       function
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SYNOPSIS

10        #include <openssl/ssl.h>
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12        void SSL_CTX_set_cert_cb(SSL_CTX *c, int (*cert_cb)(SSL *ssl, void *arg), void *arg);
13        void SSL_set_cert_cb(SSL *s, int (*cert_cb)(SSL *ssl, void *arg), void *arg);
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15        int (*cert_cb)(SSL *ssl, void *arg);
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DESCRIPTION

18       SSL_CTX_set_cert_cb() and SSL_set_cert_cb() sets the cert_cb()
19       callback, arg value is pointer which is passed to the application
20       callback.
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22       When cert_cb() is NULL, no callback function is used.
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24       cert_cb() is the application defined callback. It is called before a
25       certificate will be used by a client or server. The callback can then
26       inspect the passed ssl structure and set or clear any appropriate
27       certificates. If the callback is successful it MUST return 1 even if no
28       certificates have been set. A zero is returned on error which will
29       abort the handshake with a fatal internal error alert. A negative
30       return value will suspend the handshake and the handshake function will
31       return immediately.  SSL_get_error(3) will return
32       SSL_ERROR_WANT_X509_LOOKUP to indicate, that the handshake was
33       suspended. The next call to the handshake function will again lead to
34       the call of cert_cb(). It is the job of the cert_cb() to store
35       information about the state of the last call, if required to continue.
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NOTES

38       An application will typically call SSL_use_certificate() and
39       SSL_use_PrivateKey() to set the end entity certificate and private key.
40       It can add intermediate and optionally the root CA certificates using
41       SSL_add1_chain_cert().
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43       It might also call SSL_certs_clear() to delete any certificates
44       associated with the SSL object.
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46       The certificate callback functionality supercedes the (largely broken)
47       functionality provided by the old client certificate callback
48       interface.  It is always called even is a certificate is already set so
49       the callback can modify or delete the existing certificate.
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51       A more advanced callback might examine the handshake parameters and set
52       whatever chain is appropriate. For example a legacy client supporting
53       only TLS v1.0 might receive a certificate chain signed using SHA1
54       whereas a TLS v1.2 client which advertises support for SHA256 could
55       receive a chain using SHA256.
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57       Normal server sanity checks are performed on any certificates set by
58       the callback. So if an EC chain is set for a curve the client does not
59       support it will not be used.
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SEE ALSO

62       ssl(3), SSL_use_certificate(3), SSL_add1_chain_cert(3),
63       SSL_get_client_CA_list(3), SSL_clear(3), SSL_free(3)
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671.0.2o                            2019-09-10            SSL_CTX_set_cert_cb(3)
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