Add ability to generate the authorisation URL from the client

lib/dnsimple/client/clients.rb

@@ -16,6 +16,11 @@ def domains
       @services[:domains] ||= Client::DomainsService.new(self)
     end
 
+    # @return [Dnsimple::Client::OauthService] The oauth-related API proxy.
+    def oauth
+      @services[:oauth] ||= Client::OauthService.new(self)
+    end
+
     # @return [Dnsimple::Client::RegistrarService] The registrar-related API proxy.
     def registrar
       @services[:registrar] ||= Client::RegistrarService.new(self)
@@ -79,6 +84,13 @@ class DomainsService < ClientService
     end
 
 
+    require_relative 'oauth'
+
+    class OauthService < ClientService
+      include Client::Oauth
+    end
+
+
     require_relative 'registrar'
 
     class RegistrarService < ClientService

lib/dnsimple/client/oauth.rb

@@ -0,0 +1,25 @@
+module Dnsimple
+  class Client
+    module Oauth
+
+      # Gets the URL to authorize an user for an application via the OAuth2 flow.
+      #
+      # @see https://developer.dnsimple.com/v2/oauth/
+      #
+      # @param  client_id [String] Client Id you received when the application was registered with DNSimple.
+      # @option options [String] :redirect_uri The url to redirect to after authorizing.
+      # @option options [String] :scope The scopes to request from the user.
+      # @option options [String] :state A random string to protect against CSRF.
+      # @return [String] The url to redirect the user to authorize.
+      def authorize_url(client_id, options = {})
+        site_url = client.base_url.sub('api.', '')
+        url = URI.join(site_url, "/oauth/authorize?client_id=#{client_id}")
+        options.each do |key, value|
+          url.query += "&#{key}=#{value}"
+        end
+        url.to_s
+      end
+
+    end
+  end
+end

spec/dnsimple/client/oauth_spec.rb

@@ -0,0 +1,20 @@
+require 'spec_helper'
+
+describe Dnsimple::Client, ".oauth" do
+
+  subject { described_class.new(base_url: "https://api.dnsimple.test", access_token: "a1b2c3").oauth }
+
+
+  describe "#authorize_url" do
+    it "builds the correct url" do
+      url = subject.authorize_url("great-app")
+      expect(url).to eq("https://dnsimple.test/oauth/authorize?client_id=great-app")
+    end
+
+    it "exposes the options in the query string" do
+      url = subject.authorize_url("great-app", secret: "1", redirect_uri: "http://example.com")
+      expect(url).to eq("https://dnsimple.test/oauth/authorize?client_id=great-app&secret=1&redirect_uri=http://example.com")
+    end
+  end
+
+end