1A few things that could be hacked on.
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 3Remove httpsig key fetching from the input path.
 4	If the key is known, check signature and reply 200 or 401.
 5	If the key is unknown, immediately reply 202 and process later.
 6
 7The gob encoding for backend rpc uses more memory than needed.
 8	A custom encoding could reduce allocations.
 9	Maybe the backend could fetch the data itself.
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