upstream: document the unbound/host-bound options to

PubkeyAuthentication; spotted by HARUYAMA Seigo

OpenBSD-Commit-ID: 298f681b66a9ecd498f0700082c7a6c46e948981

ssh_config.5

@@ -33,8 +33,8 @@
 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.\" $OpenBSD: ssh_config.5,v 1.368 2022/02/04 02:49:17 dtucker Exp $
-.Dd $Mdocdate: February 4 2022 $
+.\" $OpenBSD: ssh_config.5,v 1.369 2022/02/15 05:13:36 djm Exp $
+.Dd $Mdocdate: February 15 2022 $
 .Dt SSH_CONFIG 5
 .Os
 .Sh NAME
@@ -1521,9 +1521,16 @@ The list of available signature algorithms may also be obtained using
 Specifies whether to try public key authentication.
 The argument to this keyword must be
 .Cm yes
-(the default)
+(the default),
+.Cm no ,
+.Cm unbound
 or
-.Cm no .
+.Cm host-bound .
+The final two options enable public key authentication while respectively
+disabling or enabling the OpenSSH host-bound authentication protocol
+extension required for restricted
+.Xr ssh-agent 1
+forwarding.
 .It Cm RekeyLimit
 Specifies the maximum amount of data that may be transmitted before the
 session key is renegotiated, optionally followed by a maximum amount of