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133 .\" ========================================================================
135 .IX Title "SSL_CTX_SET_CERT_CB 3"
136 .TH SSL_CTX_SET_CERT_CB 3 "2020-03-17" "1.1.1e" "OpenSSL"
137 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
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142 SSL_CTX_set_cert_cb, SSL_set_cert_cb \- handle certificate callback function
144 .IX Header "SYNOPSIS"
146 \& #include <openssl/ssl.h>
148 \& void SSL_CTX_set_cert_cb(SSL_CTX *c, int (*cert_cb)(SSL *ssl, void *arg),
150 \& void SSL_set_cert_cb(SSL *s, int (*cert_cb)(SSL *ssl, void *arg), void *arg);
152 \& int (*cert_cb)(SSL *ssl, void *arg);
155 .IX Header "DESCRIPTION"
156 \&\fBSSL_CTX_set_cert_cb()\fR and \fBSSL_set_cert_cb()\fR sets the \fBcert_cb()\fR callback,
157 \&\fBarg\fR value is pointer which is passed to the application callback.
159 When \fBcert_cb()\fR is \s-1NULL,\s0 no callback function is used.
161 \&\fBcert_cb()\fR is the application defined callback. It is called before a
162 certificate will be used by a client or server. The callback can then inspect
163 the passed \fBssl\fR structure and set or clear any appropriate certificates. If
164 the callback is successful it \fB\s-1MUST\s0\fR return 1 even if no certificates have
165 been set. A zero is returned on error which will abort the handshake with a
166 fatal internal error alert. A negative return value will suspend the handshake
167 and the handshake function will return immediately.
168 \&\fBSSL_get_error\fR\|(3) will return \s-1SSL_ERROR_WANT_X509_LOOKUP\s0 to
169 indicate, that the handshake was suspended. The next call to the handshake
170 function will again lead to the call of \fBcert_cb()\fR. It is the job of the
171 \&\fBcert_cb()\fR to store information about the state of the last call,
172 if required to continue.
175 An application will typically call \fBSSL_use_certificate()\fR and
176 \&\fBSSL_use_PrivateKey()\fR to set the end entity certificate and private key.
177 It can add intermediate and optionally the root \s-1CA\s0 certificates using
178 \&\fBSSL_add1_chain_cert()\fR.
180 It might also call \fBSSL_certs_clear()\fR to delete any certificates associated
181 with the \fB\s-1SSL\s0\fR object.
183 The certificate callback functionality supersedes the (largely broken)
184 functionality provided by the old client certificate callback interface.
185 It is \fBalways\fR called even is a certificate is already set so the callback
186 can modify or delete the existing certificate.
188 A more advanced callback might examine the handshake parameters and set
189 whatever chain is appropriate. For example a legacy client supporting only
190 TLSv1.0 might receive a certificate chain signed using \s-1SHA1\s0 whereas a
191 TLSv1.2 or later client which advertises support for \s-1SHA256\s0 could receive a
192 chain using \s-1SHA256.\s0
194 Normal server sanity checks are performed on any certificates set
195 by the callback. So if an \s-1EC\s0 chain is set for a curve the client does not
196 support it will \fBnot\fR be used.
198 .IX Header "RETURN VALUES"
199 \&\fBSSL_CTX_set_cert_cb()\fR and \fBSSL_set_cert_cb()\fR do not return values.
201 .IX Header "SEE ALSO"
202 \&\fBssl\fR\|(7), \fBSSL_use_certificate\fR\|(3),
203 \&\fBSSL_add1_chain_cert\fR\|(3),
204 \&\fBSSL_get_client_CA_list\fR\|(3),
205 \&\fBSSL_clear\fR\|(3), \fBSSL_free\fR\|(3)
207 .IX Header "COPYRIGHT"
208 Copyright 2014\-2018 The OpenSSL Project Authors. All Rights Reserved.
210 Licensed under the OpenSSL license (the \*(L"License\*(R"). You may not use
211 this file except in compliance with the License. You can obtain a copy
212 in the file \s-1LICENSE\s0 in the source distribution or at
213 <https://www.openssl.org/source/license.html>.