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Editing: SSL_set_cert_cb.3
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Always turn off hyphenation; it makes .\" way too many mistakes in technical documents. .if n .ad l .nh .SH "NAME" SSL_CTX_set_cert_cb, SSL_set_cert_cb \- handle certificate callback function .SH "SYNOPSIS" .IX Header "SYNOPSIS" .Vb 1 \& #include <openssl/ssl.h> \& \& void SSL_CTX_set_cert_cb(SSL_CTX *c, int (*cert_cb)(SSL *ssl, void *arg), void *arg); \& void SSL_set_cert_cb(SSL *s, int (*cert_cb)(SSL *ssl, void *arg), void *arg); \& \& int (*cert_cb)(SSL *ssl, void *arg); .Ve .SH "DESCRIPTION" .IX Header "DESCRIPTION" \&\fBSSL_CTX_set_cert_cb()\fR and \fBSSL_set_cert_cb()\fR sets the \fB\fBcert_cb()\fB\fR callback, \&\fBarg\fR value is pointer which is passed to the application callback. .PP When \fB\fBcert_cb()\fB\fR is \s-1NULL,\s0 no callback function is used. .PP \&\fBcert_cb()\fR is the application defined callback. It is called before a certificate will be used by a client or server. The callback can then inspect the passed \fBssl\fR structure and set or clear any appropriate certificates. If the callback is successful it \fB\s-1MUST\s0\fR return 1 even if no certificates have been set. A zero is returned on error which will abort the handshake with a fatal internal error alert. A negative return value will suspend the handshake and the handshake function will return immediately. \&\fBSSL_get_error\fR\|(3) will return \s-1SSL_ERROR_WANT_X509_LOOKUP\s0 to indicate, that the handshake was suspended. The next call to the handshake function will again lead to the call of \fBcert_cb()\fR. It is the job of the \&\fBcert_cb()\fR to store information about the state of the last call, if required to continue. .SH "NOTES" .IX Header "NOTES" An application will typically call \fBSSL_use_certificate()\fR and \&\fBSSL_use_PrivateKey()\fR to set the end entity certificate and private key. It can add intermediate and optionally the root \s-1CA\s0 certificates using \&\fBSSL_add1_chain_cert()\fR. .PP It might also call \fBSSL_certs_clear()\fR to delete any certificates associated with the \fB\s-1SSL\s0\fR object. .PP The certificate callback functionality supercedes the (largely broken) functionality provided by the old client certificate callback interface. It is \fBalways\fR called even is a certificate is already set so the callback can modify or delete the existing certificate. .PP A more advanced callback might examine the handshake parameters and set whatever chain is appropriate. For example a legacy client supporting only \&\s-1TLS\s0 v1.0 might receive a certificate chain signed using \s-1SHA1\s0 whereas a \&\s-1TLS\s0 v1.2 client which advertises support for \s-1SHA256\s0 could receive a chain using \s-1SHA256.\s0 .PP Normal server sanity checks are performed on any certificates set by the callback. So if an \s-1EC\s0 chain is set for a curve the client does not support it will \fBnot\fR be used. .SH "SEE ALSO" .IX Header "SEE ALSO" \&\fBssl\fR\|(3), \fBSSL_use_certificate\fR\|(3), \&\fBSSL_add1_chain_cert\fR\|(3), \&\fBSSL_get_client_CA_list\fR\|(3), \&\fBSSL_clear\fR\|(3), \fBSSL_free\fR\|(3)
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