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.IX Title "SSL_CTX_set_tlsext_status_cb 3"
.TH SSL_CTX_set_tlsext_status_cb 3 2019-12-20 1.0.2u OpenSSL
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH NAME
SSL_CTX_set_tlsext_status_cb, SSL_CTX_set_tlsext_status_arg,
SSL_set_tlsext_status_type, SSL_get_tlsext_status_ocsp_resp,
SSL_set_tlsext_status_ocsp_resp \- OCSP Certificate Status Request functions
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/tls1.h>
\&
\& long SSL_CTX_set_tlsext_status_cb(SSL_CTX *ctx,
\&                                   int (*callback)(SSL *, void *));
\& long SSL_CTX_set_tlsext_status_arg(SSL_CTX *ctx, void *arg);
\&
\& long SSL_set_tlsext_status_type(SSL *s, int type);
\&
\& long SSL_get_tlsext_status_ocsp_resp(ssl, unsigned char **resp);
\& long SSL_set_tlsext_status_ocsp_resp(ssl, unsigned char *resp, int len);
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
A client application may request that a server send back an OCSP status response
(also known as OCSP stapling). To do so the client should call the
\&\fBSSL_set_tlsext_status_type()\fR function prior to the start of the handshake.
Currently the only supported type is \fBTLSEXT_STATUSTYPE_ocsp\fR. This value
should be passed in the \fBtype\fR argument. The client should additionally provide
a callback function to decide what to do with the returned OCSP response by
calling \fBSSL_CTX_set_tlsext_status_cb()\fR. The callback function should determine
whether the returned OCSP response is acceptable or not. The callback will be
passed as an argument the value previously set via a call to
\&\fBSSL_CTX_set_tlsext_status_arg()\fR. Note that the callback will not be called in
the event of a handshake where session resumption occurs (because there are no
Certificates exchanged in such a handshake).
.PP
The response returned by the server can be obtained via a call to
\&\fBSSL_get_tlsext_status_ocsp_resp()\fR. The value \fB*resp\fR will be updated to point
to the OCSP response data and the return value will be the length of that data.
Typically a callback would obtain an OCSP_RESPONSE object from this data via a
call to the \fBd2i_OCSP_RESPONSE()\fR function. If the server has not provided any
response data then \fB*resp\fR will be NULL and the return value from
\&\fBSSL_get_tlsext_status_ocsp_resp()\fR will be \-1.
.PP
A server application must also call the \fBSSL_CTX_set_tlsext_status_cb()\fR function
if it wants to be able to provide clients with OCSP Certificate Status
responses. Typically the server callback would obtain the server certificate
that is being sent back to the client via a call to \fBSSL_get_certificate()\fR;
obtain the OCSP response to be sent back; and then set that response data by
calling \fBSSL_set_tlsext_status_ocsp_resp()\fR. A pointer to the response data should
be provided in the \fBresp\fR argument, and the length of that data should be in
the \fBlen\fR argument.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
The callback when used on the client side should return a negative value on
error; 0 if the response is not acceptable (in which case the handshake will
fail) or a positive value if it is acceptable.
.PP
The callback when used on the server side should return with either
SSL_TLSEXT_ERR_OK (meaning that the OCSP response that has been set should be
returned), SSL_TLSEXT_ERR_NOACK (meaning that an OCSP response should not be
returned) or SSL_TLSEXT_ERR_ALERT_FATAL (meaning that a fatal error has
occurred).
.PP
\&\fBSSL_CTX_set_tlsext_status_cb()\fR, \fBSSL_CTX_set_tlsext_status_arg()\fR,
\&\fBSSL_set_tlsext_status_type()\fR and \fBSSL_set_tlsext_status_ocsp_resp()\fR return 0 on
error or 1 on success.
.PP
\&\fBSSL_get_tlsext_status_ocsp_resp()\fR returns the length of the OCSP response data
or \-1 if there is no OCSP response data.