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131 .IX Title "SSL_CTX_set_cert_cb 3"
132 .TH SSL_CTX_set_cert_cb 3 "2018-08-14" "1.0.2p" "OpenSSL"
133 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
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138 SSL_CTX_set_cert_cb, SSL_set_cert_cb \- handle certificate callback function
140 .IX Header "SYNOPSIS"
142 \& #include <openssl/ssl.h>
144 \& void SSL_CTX_set_cert_cb(SSL_CTX *c, int (*cert_cb)(SSL *ssl, void *arg), void *arg);
145 \& void SSL_set_cert_cb(SSL *s, int (*cert_cb)(SSL *ssl, void *arg), void *arg);
147 \& int (*cert_cb)(SSL *ssl, void *arg);
150 .IX Header "DESCRIPTION"
151 \&\fISSL_CTX_set_cert_cb()\fR and \fISSL_set_cert_cb()\fR sets the \fB\f(BIcert_cb()\fB\fR callback,
152 \&\fBarg\fR value is pointer which is passed to the application callback.
154 When \fB\f(BIcert_cb()\fB\fR is \s-1NULL,\s0 no callback function is used.
156 \&\fIcert_cb()\fR is the application defined callback. It is called before a
157 certificate will be used by a client or server. The callback can then inspect
158 the passed \fBssl\fR structure and set or clear any appropriate certificates. If
159 the callback is successful it \fB\s-1MUST\s0\fR return 1 even if no certificates have
160 been set. A zero is returned on error which will abort the handshake with a
161 fatal internal error alert. A negative return value will suspend the handshake
162 and the handshake function will return immediately.
163 \&\fISSL_get_error\fR\|(3) will return \s-1SSL_ERROR_WANT_X509_LOOKUP\s0 to
164 indicate, that the handshake was suspended. The next call to the handshake
165 function will again lead to the call of \fIcert_cb()\fR. It is the job of the
166 \&\fIcert_cb()\fR to store information about the state of the last call,
167 if required to continue.
170 An application will typically call \fISSL_use_certificate()\fR and
171 \&\fISSL_use_PrivateKey()\fR to set the end entity certificate and private key.
172 It can add intermediate and optionally the root \s-1CA\s0 certificates using
173 \&\fISSL_add1_chain_cert()\fR.
175 It might also call \fISSL_certs_clear()\fR to delete any certificates associated
176 with the \fB\s-1SSL\s0\fR object.
178 The certificate callback functionality supercedes the (largely broken)
179 functionality provided by the old client certificate callback interface.
180 It is \fBalways\fR called even is a certificate is already set so the callback
181 can modify or delete the existing certificate.
183 A more advanced callback might examine the handshake parameters and set
184 whatever chain is appropriate. For example a legacy client supporting only
185 \&\s-1TLS\s0 v1.0 might receive a certificate chain signed using \s-1SHA1\s0 whereas a
186 \&\s-1TLS\s0 v1.2 client which advertises support for \s-1SHA256\s0 could receive a chain
189 Normal server sanity checks are performed on any certificates set
190 by the callback. So if an \s-1EC\s0 chain is set for a curve the client does not
191 support it will \fBnot\fR be used.
193 .IX Header "SEE ALSO"
194 \&\fIssl\fR\|(3), \fISSL_use_certificate\fR\|(3),
195 \&\fISSL_add1_chain_cert\fR\|(3),
196 \&\fISSL_get_client_CA_list\fR\|(3),
197 \&\fISSL_clear\fR\|(3), \fISSL_free\fR\|(3)