OAuth authentication

[jacegu]

Support for OAuth-based authentication in API v2

[jacegu]

@weppos not sure what's the role of Dnsimple::Compatibility class. There are references to both: api_token and exchange_token.

The User struct also includes the api_token attribute which I'm not sure whether it will stick around.

[jacegu]

I am having second thoughts against removing oauth_client_id and oauth_client_secret as configuration parameters for the client. I think it's more convenient to have them there via the environment variables than to having to pull them every time you want to get an access token.

I'll leave them there for now and we can go back to them before closing this PR.

[weppos]

@jacegu Dnsimple::Compatibility was introduced as a bridge between the API client v1.x and v2. It should be removed for the new version.

[jacegu]

I'd like to have the knowledge of what endpoint to hit to make the OAuth login in the client itself. I think it's convenient as a client user to have it there... It would be something similar to (extracted from an spike):

def authorize_url
  "#{@url}:#{@port}/oauth/authorize?client_id=#{@client_id}&response_type=code&state=1234567"
end

@weppos how do you feel about it?

[weppos]

Yes, it may be useful.

But I have to ask you to hold off until the Oauth is properly documented and completed. The OAuth controller in fact is still incomplete, and it may result into an incomplete or inefficient implementation in the client.

[jacegu]

With the changes in place you can see this working locally:

$: << 'lib'
require 'dnsimple'

client = Dnsimple::Client.new(oauth_access_token: "XXX")
puts client.get("/v2/1/domains")