When constructing a Context from a HeaderMap, fill in the env_config field

[khuey]

Description of changes: Currently this just produces a useless env_config.

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[rimutaka]

Good spotting!

We also missed pub client_context: Option<ClientContext> and pub identity: Option<CognitoIdentity> in the same Context structure.
They are declared, but are never used. I'll need both of them in a few weeks, so if no one fixes it by then I'll have to :)

[khuey]

Doesn't look like ClientContext or CognitoIdentity have any existing from_the_relevant_thing methods though, so I'd prefer just to merge this as is :)

[khuey]

Ping?

[davidbarsky]

Apologies for the delay, @khuey. I spoke too soon in saying that I'm happy to merge this; just one comment though.

[davidbarsky]

Thanks!

[khuey]

Anybody going to merge this?