Public: Uses the simple_oauth library to sign requests according the OAuth protocol.

The options for this middleware are forwarded to SimpleOAuth::Header: :consumer_key, :consumer_secret, :token, :token_secret. All these parameters are optional.

The signature is added to the "Authorization" HTTP request header. If the value for this header already exists, it is not overriden.

If no Content-Type header is specified, this middleware assumes that request body parameters should be included while signing the request. Otherwise, it only includes them if the Content-Type is "application/x-www-form-urlencoded", as per OAuth 1.0.

For better performance while signing requests, this middleware should be positioned before UrlEncoded middleware on the stack, but after any other body-encoding middleware (such as EncodeJson).