Overview

The connection

NXOAuth2Connection is a wrapper around NXURLConnection.
It's main purpose is to simplify the delegates & to provide a context
ivar that can be used to put a connection object in a certain context.
The context may be compared to a tag.

NXOAuth2Connection only provides asynchronous connections as synchronous
connections are strongly discouraged.

The connection works together with the OAuth2 Client to sign a request
before sending it. If no client is passed in the connection will sent
unsigned requests.