Investigation into undocumented ssh_config and sshd_config options, as of https://github.com/openssh/openssh-portable/tree/e6c85f8889c5c9eb04796fdb76d2807636b9eef5 Scroll to bottom for the upshot

all_client_options

addkeystoagent
addressfamily
afstokenpassing
batchmode
bindaddress
canonicaldomains
canonicalizefallbacklocal
canonicalizehostname
canonicalizemaxdots
canonicalizepermittedcnames
certificatefile
challengeresponseauthentication
checkhostip
cipher
ciphers
clearallforwardings
compression
compressionlevel
connectionattempts
connecttimeout
controlmaster
controlpath
controlpersist
dsaauthentication
dynamicforward
enablesshkeysign
escapechar
exitonforwardfailure
fallbacktorsh
fingerprinthash
forwardagent
forwardx11
forwardx11timeout
forwardx11trusted
gatewayports
globalknownhostsfile
globalknownhostsfile2
gssapiauthentication
gssapidelegatecredentials
hashknownhosts
host
hostbasedauthentication
hostbasedkeytypes
hostkeyalgorithms
hostkeyalias
hostname
identitiesonly
identityfile
identityfile2
ignoreunknown
ipqos
kbdinteractiveauthentication
kbdinteractivedevices
keepalive
kerberosauthentication
kerberostgtpassing
kexalgorithms
localcommand
localforward
loglevel
macs
match
nohostauthenticationforlocalhost
numberofpasswordprompts
passwordauthentication
permitlocalcommand
pkcs11provider
port
preferredauthentications
protocol
proxycommand
proxyusefdpass
pubkeyacceptedkeytypes
pubkeyauthentication
rekeylimit
remoteforward
requesttty
revokedhostkeys
rhostsauthentication
rhostsrsaauthentication
rsaauthentication
sendenv
serveralivecountmax
serveraliveinterval
skeyauthentication
smartcarddevice
streamlocalbindmask
streamlocalbindunlink
stricthostkeychecking
tcpkeepalive
tisauthentication
tunnel
tunneldevice
updatehostkeys
useprivilegedport
user
userknownhostsfile
userknownhostsfile2
useroaming
usersh
verifyhostkeydns
visualhostkey
xauthlocation

all_server_options

acceptenv
addressfamily
afstokenpassing
allowagentforwarding
allowgroups
allowstreamlocalforwarding
allowtcpforwarding
allowusers
authenticationmethods
authorizedkeyscommand
authorizedkeyscommanduser
authorizedkeysfile
authorizedkeysfile2
authorizedprincipalscommand
authorizedprincipalscommanduser
authorizedprincipalsfile
banner
challengeresponseauthentication
checkmail
chrootdirectory
ciphers
clientalivecountmax
clientaliveinterval
compression
denygroups
denyusers
dsaauthentication
fingerprinthash
forcecommand
gatewayports
gssapiauthentication
gssapicleanupcredentials
gssapistrictacceptorcheck
hostbasedacceptedkeytypes
hostbasedauthentication
hostbasedusesnamefrompacketonly
hostcertificate
hostdsakey
hostkey
hostkeyagent
hostkeyalgorithms
ignorerhosts
ignoreuserknownhosts
ipqos
kbdinteractiveauthentication
keepalive
kerberosauthentication
kerberosgetafstoken
kerberosorlocalpasswd
kerberostgtpassing
kerberosticketcleanup
kexalgorithms
keyregenerationinterval
listenaddress
logingracetime
loglevel
macs
match
maxauthtries
maxsessions
maxstartups
pamauthenticationviakbdint
passwordauthentication
permitemptypasswords
permitopen
permitrootlogin
permittty
permittunnel
permituserenvironment
permituserrc
pidfile
port
printlastlog
printmotd
protocol
pubkeyacceptedkeytypes
pubkeyauthentication
rekeylimit
reversemappingcheck
revokedkeys
rhostsauthentication
rhostsrsaauthentication
rsaauthentication
serverkeybits
skeyauthentication
streamlocalbindmask
streamlocalbindunlink
strictmodes
subsystem
syslogfacility
tcpkeepalive
trustedusercakeys
usedns
uselogin
usepam
useprivilegeseparation
verifyreversemapping
versionaddendum
x11displayoffset
x11forwarding
x11uselocalhost
xauthlocation

check_manpage.sh

#!/bin/sh

while read option
do
	if ! fgrep -i "Cm $option" "$1" >/dev/null
	then
		echo "$option"
	fi
done

undocumented_client_options

afstokenpassing			unsupported (raises error if set)
dsaauthentication		alias for pubkeyauthentication
fallbacktorsh			deprecated (ignored with warning if set)
globalknownhostsfile2		deprecated
identityfile2			alias for identityfile
keepalive			alias for tcpkeepalive
kerberosauthentication		unsupported
kerberostgtpassing		unsupported
rhostsauthentication		deprecated
skeyauthentication		alias for challengeresponseauthentication
smartcarddevice			alias for pkcs11provider
tisauthentication		alias for challengeresponseauthentication
userknownhostsfile2		deprecated
useroaming			UNDOCUMENTED!!!!
usersh				deprecated

undocumented_server_options

afstokenpassing			unsupported (ignored with warning if set)
authorizedkeysfile2		deprecated (ignored with warning if set)
checkmail			deprecated
dsaauthentication		alias for pubkeyauthentication
hostdsakey			alias for hostkey
keepalive			alias for tcpkeepalive
kerberostgtpassing		unsupported
pamauthenticationviakbdint	deprecated
reversemappingcheck		deprecated
rhostsauthentication		deprecated
skeyauthentication		alias for challengeresponseauthentication
verifyreversemapping		deprecated