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Diffstat (limited to 'openssl/doc/ssl/SSL_CTX_set_client_cert_cb.pod')
-rw-r--r-- | openssl/doc/ssl/SSL_CTX_set_client_cert_cb.pod | 94 |
1 files changed, 94 insertions, 0 deletions
diff --git a/openssl/doc/ssl/SSL_CTX_set_client_cert_cb.pod b/openssl/doc/ssl/SSL_CTX_set_client_cert_cb.pod new file mode 100644 index 0000000..d0df69a --- /dev/null +++ b/openssl/doc/ssl/SSL_CTX_set_client_cert_cb.pod @@ -0,0 +1,94 @@ +=pod + +=head1 NAME + +SSL_CTX_set_client_cert_cb, SSL_CTX_get_client_cert_cb - handle client certificate callback function + +=head1 SYNOPSIS + + #include <openssl/ssl.h> + + void SSL_CTX_set_client_cert_cb(SSL_CTX *ctx, int (*client_cert_cb)(SSL *ssl, X509 **x509, EVP_PKEY **pkey)); + int (*SSL_CTX_get_client_cert_cb(SSL_CTX *ctx))(SSL *ssl, X509 **x509, EVP_PKEY **pkey); + int (*client_cert_cb)(SSL *ssl, X509 **x509, EVP_PKEY **pkey); + +=head1 DESCRIPTION + +SSL_CTX_set_client_cert_cb() sets the B<client_cert_cb()> callback, that is +called when a client certificate is requested by a server and no certificate +was yet set for the SSL object. + +When B<client_cert_cb()> is NULL, no callback function is used. + +SSL_CTX_get_client_cert_cb() returns a pointer to the currently set callback +function. + +client_cert_cb() is the application defined callback. If it wants to +set a certificate, a certificate/private key combination must be set +using the B<x509> and B<pkey> arguments and "1" must be returned. The +certificate will be installed into B<ssl>, see the NOTES and BUGS sections. +If no certificate should be set, "0" has to be returned and no certificate +will be sent. A negative return value will suspend the handshake and the +handshake function will return immediately. L<SSL_get_error(3)|SSL_get_error(3)> +will return SSL_ERROR_WANT_X509_LOOKUP to indicate, that the handshake was +suspended. The next call to the handshake function will again lead to the call +of client_cert_cb(). It is the job of the client_cert_cb() to store information +about the state of the last call, if required to continue. + +=head1 NOTES + +During a handshake (or renegotiation) a server may request a certificate +from the client. A client certificate must only be sent, when the server +did send the request. + +When a certificate was set using the +L<SSL_CTX_use_certificate(3)|SSL_CTX_use_certificate(3)> family of functions, +it will be sent to the server. The TLS standard requires that only a +certificate is sent, if it matches the list of acceptable CAs sent by the +server. This constraint is violated by the default behavior of the OpenSSL +library. Using the callback function it is possible to implement a proper +selection routine or to allow a user interaction to choose the certificate to +be sent. + +If a callback function is defined and no certificate was yet defined for the +SSL object, the callback function will be called. +If the callback function returns a certificate, the OpenSSL library +will try to load the private key and certificate data into the SSL +object using the SSL_use_certificate() and SSL_use_private_key() functions. +Thus it will permanently install the certificate and key for this SSL +object. It will not be reset by calling L<SSL_clear(3)|SSL_clear(3)>. +If the callback returns no certificate, the OpenSSL library will not send +a certificate. + +=head1 BUGS + +The client_cert_cb() cannot return a complete certificate chain, it can +only return one client certificate. If the chain only has a length of 2, +the root CA certificate may be omitted according to the TLS standard and +thus a standard conforming answer can be sent to the server. For a +longer chain, the client must send the complete chain (with the option +to leave out the root CA certificate). This can only be accomplished by +either adding the intermediate CA certificates into the trusted +certificate store for the SSL_CTX object (resulting in having to add +CA certificates that otherwise maybe would not be trusted), or by adding +the chain certificates using the +L<SSL_CTX_add_extra_chain_cert(3)|SSL_CTX_add_extra_chain_cert(3)> +function, which is only available for the SSL_CTX object as a whole and that +therefore probably can only apply for one client certificate, making +the concept of the callback function (to allow the choice from several +certificates) questionable. + +Once the SSL object has been used in conjunction with the callback function, +the certificate will be set for the SSL object and will not be cleared +even when L<SSL_clear(3)|SSL_clear(3)> is being called. It is therefore +mandatory to destroy the SSL object using L<SSL_free(3)|SSL_free(3)> +and create a new one to return to the previous state. + +=head1 SEE ALSO + +L<ssl(3)|ssl(3)>, L<SSL_CTX_use_certificate(3)|SSL_CTX_use_certificate(3)>, +L<SSL_CTX_add_extra_chain_cert(3)|SSL_CTX_add_extra_chain_cert(3)>, +L<SSL_get_client_CA_list(3)|SSL_get_client_CA_list(3)>, +L<SSL_clear(3)|SSL_clear(3)>, L<SSL_free(3)|SSL_free(3)> + +=cut |