The value of tmnxKeyChainAuthenticationKey specifies the key that
will be used by the encryption algorithm specified by
tmnxKeyChainKeyAlgorithm. tmnxKeyChainAuthenticationKey is used
to sign and authenticate a protocol packet.
The value of tmnxKeyChainAuthenticationKey can be any combination
of letters or numbers. Note that the string may contain embedded nulls.
tmnxKeyChainAuthenticationKey and tmnxKeyChainKeyAlgorithm, which
indicates the encryption algorithm to be used, must be set together in
the same SNMP request PDU or else the set request will fail with an
inconsistentValue error.
When read, tmnxKeyChainAuthenticationKey always returns an Octet
string of length zero.