Supporting Excon

[stiak]

I'd like to add support for https://github.com/excon/excon, but it doesn't follow the current model of having a request object to decorate. Instead it uses a parameter hash to pass through headers, body, request method, etc.

It seems less than ideal to map any instance of a hash passed to ApiAuth to an excon request driver.

Excon does support middleware, so I was thinking I could build a middleware, then an class that wrapped the params hash, then support mapping that to an excon request driver. So approximately three new classes. I think ApiAuth is the right home for those classes.

I can create a PR to demonstrate the change, but it would mean for excon support people would have to add the middleware rather than call sign directly.

Is that the right approach? Any other suggestions?