=pod

=head1 NAME

SSL_CTX_set_client_CA_list, SSL_set_client_CA_list, SSL_CTX_add_client_CA,
SSL_add_client_CA - set list of CAs sent to the client when requesting a
client certificate

=head1 SYNOPSIS

 #include <openssl/ssl.h>
 
 void SSL_CTX_set_client_CA_list(SSL_CTX *ctx, STACK_OF(X509_NAME) *list);
 void SSL_set_client_CA_list(SSL *s, STACK_OF(X509_NAME) *list);
 int SSL_CTX_add_client_CA(SSL_CTX *ctx, X509 *cacert);
 int SSL_add_client_CA(SSL *ssl, X509 *cacert);

=head1 DESCRIPTION

SSL_CTX_set_client_CA_list() sets the B<list> of CAs sent to the client when
requesting a client certificate for B<ctx>.

SSL_set_client_CA_list() sets the B<list> of CAs sent to the client when
requesting a client certificate for the chosen B<ssl>, overriding the
setting valid for B<ssl>'s SSL_CTX object.

SSL_CTX_add_client_CA() adds the CA name extracted from B<cacert> to the
list of CAs sent to the client when requesting a client certificate for
B<ctx>.

SSL_add_client_CA() adds the CA name extracted from B<cacert> to the
list of CAs sent to the client when requesting a client certificate for
the chosen B<ssl>, overriding the setting valid for B<ssl>'s SSL_CTX object.

=head1 NOTES

When a TLS/SSL server requests a client certificate (see
B<SSL_CTX_set_verify_options()>), it sends a list of CAs, for which
it will accept certificates, to the client.

This list must explicitly be set using SSL_CTX_set_client_CA_list() for
B<ctx> and SSL_set_client_CA_list() for the specific B<ssl>. The list
specified overrides the previous setting. The CAs listed do not become
trusted (B<list> only contains the names, not the complete certificates); use
L<SSL_CTX_load_verify_locations(3)|SSL_CTX_load_verify_locations(3)> 
to additionally load them for verification.

If the list of acceptable CAs is compiled in a file, the
L<SSL_load_client_CA_file(3)|SSL_load_client_CA_file(3)>
function can be used to help importing the necessary data.

SSL_CTX_add_client_CA() and SSL_add_client_CA() can be used to add additional
items the list of client CAs. If no list was specified before using
SSL_CTX_set_client_CA_list() or SSL_set_client_CA_list(), a new client
CA list for B<ctx> or B<ssl> (as appropriate) is opened.

These functions are only useful for TLS/SSL servers.

=head1 RETURN VALUES

SSL_CTX_set_client_CA_list() and SSL_set_client_CA_list() do not return
diagnostic information.

SSL_CTX_add_client_CA() and SSL_add_client_CA() have the following return
values:

=over 4

=item 1

The operation succeeded.

=item 0

A failure while manipulating the STACK_OF(X509_NAME) object occurred or
the X509_NAME could not be extracted from B<cacert>. Check the error stack
to find out the reason.

=back

=head1 EXAMPLES

Scan all certificates in B<CAfile> and list them as acceptable CAs:

  SSL_CTX_set_client_CA_list(ctx,SSL_load_client_CA_file(CAfile));

=head1 SEE ALSO

L<ssl(3)|ssl(3)>,
L<SSL_get_client_CA_list(3)|SSL_get_client_CA_list(3)>,
L<SSL_load_client_CA_file(3)|SSL_load_client_CA_file(3)>,
L<SSL_CTX_load_verify_locations(3)|SSL_CTX_load_verify_locations(3)>

=cut
