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X509_STORE_CTX_SET_VERIFY_CB(3)	    OpenSSL    X509_STORE_CTX_SET_VERIFY_CB(3)

NAME
       X509_STORE_CTX_get_cleanup, X509_STORE_CTX_get_lookup_crls,
       X509_STORE_CTX_get_lookup_certs,	X509_STORE_CTX_get_check_policy,
       X509_STORE_CTX_get_cert_crl, X509_STORE_CTX_get_check_crl,
       X509_STORE_CTX_get_get_crl, X509_STORE_CTX_get_check_revocation,
       X509_STORE_CTX_get_check_issued,	X509_STORE_CTX_get_get_issuer,
       X509_STORE_CTX_get_verify_cb, X509_STORE_CTX_set_verify_cb,
       X509_STORE_CTX_verify_cb	- get and set verification callback

SYNOPSIS
	#include <openssl/x509_vfy.h>

	typedef	int (*X509_STORE_CTX_verify_cb)(int, X509_STORE_CTX *);

	X509_STORE_CTX_verify_cb X509_STORE_CTX_get_verify_cb(X509_STORE_CTX *ctx);

	void X509_STORE_CTX_set_verify_cb(X509_STORE_CTX *ctx,
					  X509_STORE_CTX_verify_cb verify_cb);

	X509_STORE_CTX_get_issuer_fn X509_STORE_CTX_get_get_issuer(X509_STORE_CTX *ctx);
	X509_STORE_CTX_check_issued_fn X509_STORE_CTX_get_check_issued(X509_STORE_CTX *ctx);
	X509_STORE_CTX_check_revocation_fn X509_STORE_CTX_get_check_revocation(X509_STORE_CTX *ctx);
	X509_STORE_CTX_get_crl_fn X509_STORE_CTX_get_get_crl(X509_STORE_CTX *ctx);
	X509_STORE_CTX_check_crl_fn X509_STORE_CTX_get_check_crl(X509_STORE_CTX	*ctx);
	X509_STORE_CTX_cert_crl_fn X509_STORE_CTX_get_cert_crl(X509_STORE_CTX *ctx);
	X509_STORE_CTX_check_policy_fn X509_STORE_CTX_get_check_policy(X509_STORE_CTX *ctx);
	X509_STORE_CTX_lookup_certs_fn X509_STORE_CTX_get_lookup_certs(X509_STORE_CTX *ctx);
	X509_STORE_CTX_lookup_crls_fn X509_STORE_CTX_get_lookup_crls(X509_STORE_CTX *ctx);
	X509_STORE_CTX_cleanup_fn X509_STORE_CTX_get_cleanup(X509_STORE_CTX *ctx);

DESCRIPTION
       X509_STORE_CTX_set_verify_cb() sets the verification callback of	ctx to
       verify_cb overwriting any existing callback.

       The verification	callback can be	used to	customise the operation	of
       certificate verification, either	by overriding error conditions or
       logging errors for debugging purposes.

       However a verification callback is not essential	and the	default
       operation is often sufficient.

       The ok parameter	to the callback	indicates the value the	callback
       should return to	retain the default behaviour. If it is zero then an
       error condition is indicated. If	it is 1	then no	error occurred.	If the
       flag X509_V_FLAG_NOTIFY_POLICY is set then ok is	set to 2 to indicate
       the policy checking is complete.

       The ctx parameter to the	callback is the	X509_STORE_CTX structure that
       is performing the verification operation. A callback can	examine	this
       structure and receive additional	information about the error, for
       example by calling X509_STORE_CTX_get_current_cert(). Additional
       application data	can be passed to the callback via the ex_data
       mechanism.

       X509_STORE_CTX_get_verify_cb() returns the value	of the current
       callback	for the	specific ctx.

       X509_STORE_CTX_get_get_issuer(),	X509_STORE_CTX_get_check_issued(),
       X509_STORE_CTX_get_check_revocation(), X509_STORE_CTX_get_get_crl(),
       X509_STORE_CTX_get_check_crl(), X509_STORE_CTX_get_cert_crl(),
       X509_STORE_CTX_get_check_policy(), X509_STORE_CTX_get_lookup_certs(),
       X509_STORE_CTX_get_lookup_crls()	and X509_STORE_CTX_get_cleanup()
       return the function pointers cached from	the corresponding X509_STORE,
       please see X509_STORE_set_verify(3) for more information.

WARNING
       In general a verification callback should NOT unconditionally return 1
       in all circumstances because this will allow verification to succeed no
       matter what the error. This effectively removes all security from the
       application because any certificate (including untrusted	generated
       ones) will be accepted.

NOTES
       The verification	callback can be	set and	inherited from the parent
       structure performing the	operation. In some cases (such as S/MIME
       verification) the X509_STORE_CTX	structure is created and destroyed
       internally and the only way to set a custom verification	callback is by
       inheriting it from the associated X509_STORE.

RETURN VALUES
       X509_STORE_CTX_set_verify_cb() does not return a	value.

EXAMPLES
       Default callback	operation:

	int verify_callback(int	ok, X509_STORE_CTX *ctx) {
	    return ok;
	}

       Simple example, suppose a certificate in	the chain is expired and we
       wish to continue	after this error:

	int verify_callback(int	ok, X509_STORE_CTX *ctx) {
	    /* Tolerate	certificate expiration */
	    if (X509_STORE_CTX_get_error(ctx) == X509_V_ERR_CERT_HAS_EXPIRED)
		return 1;
	    /* Otherwise don't override	*/
	    return ok;
	}

       More complex example, we	don't wish to continue after any certificate
       has expired just	one specific case:

	int verify_callback(int	ok, X509_STORE_CTX *ctx)
	{
	    int	err = X509_STORE_CTX_get_error(ctx);
	    X509 *err_cert = X509_STORE_CTX_get_current_cert(ctx);

	    if (err == X509_V_ERR_CERT_HAS_EXPIRED) {
		if (check_is_acceptable_expired_cert(err_cert)
		    return 1;
	    }
	    return ok;
	}

       Full featured logging callback. In this case the	bio_err	is assumed to
       be a global logging BIO,	an alternative would to	store a	BIO in ctx
       using ex_data.

	int verify_callback(int	ok, X509_STORE_CTX *ctx)
	{
	    X509 *err_cert;
	    int	err, depth;

	    err_cert = X509_STORE_CTX_get_current_cert(ctx);
	    err	= X509_STORE_CTX_get_error(ctx);
	    depth = X509_STORE_CTX_get_error_depth(ctx);

	    BIO_printf(bio_err,	"depth=%d ", depth);
	    if (err_cert) {
		X509_NAME_print_ex(bio_err, X509_get_subject_name(err_cert),
				   0, XN_FLAG_ONELINE);
		BIO_puts(bio_err, "\n");
	    }
	    else
		BIO_puts(bio_err, "<no cert>\n");
	    if (!ok)
		BIO_printf(bio_err, "verify error:num=%d:%s\n",	err,
			   X509_verify_cert_error_string(err));
	    switch (err) {
	    case X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT:
		BIO_puts(bio_err, "issuer= ");
		X509_NAME_print_ex(bio_err, X509_get_issuer_name(err_cert),
				   0, XN_FLAG_ONELINE);
		BIO_puts(bio_err, "\n");
		break;
	    case X509_V_ERR_CERT_NOT_YET_VALID:
	    case X509_V_ERR_ERROR_IN_CERT_NOT_BEFORE_FIELD:
		BIO_printf(bio_err, "notBefore=");
		ASN1_TIME_print(bio_err, X509_get_notBefore(err_cert));
		BIO_printf(bio_err, "\n");
		break;
	    case X509_V_ERR_CERT_HAS_EXPIRED:
	    case X509_V_ERR_ERROR_IN_CERT_NOT_AFTER_FIELD:
		BIO_printf(bio_err, "notAfter=");
		ASN1_TIME_print(bio_err, X509_get_notAfter(err_cert));
		BIO_printf(bio_err, "\n");
		break;
	    case X509_V_ERR_NO_EXPLICIT_POLICY:
		policies_print(bio_err,	ctx);
		break;
	    }
	    if (err == X509_V_OK && ok == 2)
		/* print out policies */

	    BIO_printf(bio_err,	"verify	return:%d\n", ok);
	    return(ok);
	}

SEE ALSO
       X509_STORE_CTX_get_error(3) X509_STORE_set_verify_cb_func(3)
       X509_STORE_CTX_get_ex_new_index(3)

HISTORY
       X509_STORE_CTX_get_get_issuer(),	X509_STORE_CTX_get_check_issued(),
       X509_STORE_CTX_get_check_revocation(), X509_STORE_CTX_get_get_crl(),
       X509_STORE_CTX_get_check_crl(), X509_STORE_CTX_get_cert_crl(),
       X509_STORE_CTX_get_check_policy(), X509_STORE_CTX_get_lookup_certs(),
       X509_STORE_CTX_get_lookup_crls()	and X509_STORE_CTX_get_cleanup() were
       added in	OpenSSL	1.1.0.

COPYRIGHT
       Copyright 2009-2016 The OpenSSL Project Authors.	All Rights Reserved.

       Licensed	under the OpenSSL license (the "License").  You	may not	use
       this file except	in compliance with the License.	 You can obtain	a copy
       in the file LICENSE in the source distribution or at
       <https://www.openssl.org/source/license.html>.

1.1.1a				  2018-11-20   X509_STORE_CTX_SET_VERIFY_CB(3)

NAME | SYNOPSIS | DESCRIPTION | WARNING | NOTES | RETURN VALUES | EXAMPLES | SEE ALSO | HISTORY | COPYRIGHT

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