Callback right after an Easy is Assigned a Connection?

HMAC Authorization Headers, like Amazon's AWS v2, encode the 'Date:' header
in the calculation allowing requests to have a TTL.

Currently we are generating the 'Authorization:' header before submitting
the easy handle to our multi handle. While this has been working for us,
we've had several events where the multi's backlog of easy handles is long
enough that the HMAC TTL expires. We don't have HTTP/1.1 pipelining enabled
(got the impression pipelining is being removed from libcurl), and do set
connection limits to help keep our clients from overloading servers.

Questions:
1. Are we doing this wrong? Manually setting the Date header and
calculating the HMAC before submitting? We still support older curls and
haven't looked into newer features, as old as v7.29 sadly.
2. Is there a straight forward way for curl to inform an application that
it is ready to use a connection, allowing the application to alter the
headers?

I've crawled the curl_easy_setopt options a couple times and nothing has
jumped out at me.

Thanks in advance for your time and expertise!
Damon

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Received on 2020-06-15