[exim] can't "hide" a macro value in config file

Following the example given in the description of the ${hmac} function
in the spec, I'd like to set a MACRO to hold the secret. I've just
found that I can't preface it with the "hide" modifier; exim complains
that the MACRO name is not a recognized option.

That's too bad, since I'd like to protect my secret.  Any way to use
"hide" with a macro definition?
-- 
bill-exim@??? (WJCarpenter)    PGP 0x91865119
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