Send unsigned

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This came up when @pbrisbin was adding SSO support - it would be nice to have an easy interface to send unsigned requests, in case AWS stand up more exotic auth methods.

I also refactored STS and SSO to use it.

• Use EnvNoAuth in public type signatures
• Remove Foldable withAuth from fromSSO
• Remove Foldable withAuth from fromWebIdentity

Closes #758

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@pbrisbin We talked about doing this when you wrote up the SSO stuff - do you have time to take a look?

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@pbrisbin What if, instead of requiring EnvNoAuth in sendUnsigned, I do the env {envAuth = Proxy} override inside sendUnsigned instead of the SSO/STS functions? This would give a more consistent interface and involve less type magic.

I think I will do this tomorrow.

[pbrisbin]

That does seem reasonable to me. I think seeing sendUnsigned :: Env' withAuth better indicates "I'm going to ignore whatever auth there is", but you really have to understand how this library works to hear what it's saying, so 🤷

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I'm much happier with how this turned out. Thanks for your input.