I could understand that currently we cannot easily pass this kind of header:

    Authorization: Token token=...

unless we make `access_token = "token=#{access_token}"` and `access_token_type = 'Token'`
What I tried to follow here is the spec from RFC: http://tools.ietf.org/html/rfc6749
And I would avoid some implementation specific stuffs like Instagram here.

I could tell this kind of format is actually in spec from [7.1. Access Token Types](http://tools.ietf.org/html/rfc6749#section-7.1):

     GET /resource/1 HTTP/1.1
     Host: example.com
     Authorization: MAC id="h480djs93hd8",
                        nonce="274312:dj83hs9s",
                        mac="kDZvddkndxvhGRXZhvuDjEWhGeE="

As you can see, the access token could actually be a hash, not a single value.
Maybe we could detect if the access token is actually a hash, then we could
build this instead.

I could work on this.