add endpoint for initial authorization

lib/travis/api/app/endpoint/authorization.rb

@@ -77,7 +77,26 @@ class Travis::Api::App
         { 'access_token' => github_to_travis(params[:token], app_id: 1) }
       end
 
+      get '/handshake' do
+        handshake do |*, redirect_uri|
+          redirect redirect_uri
+        end
+      end
+
       get '/post_message' do
+        handshake do |user, token|
+          rendered_user = service(:user, user).find_one
+          post_message(token: token, user: rendered_user)
+        end
+      end
+
+      error Faraday::Error::ClientError do
+        halt 401, 'could not resolve github token'
+      end
+
+      private
+
+        def handshake
           config   = Travis.config.oauth2
           endpoint = Addressable::URI.parse(config.authorization_server)
           values   = {
@@ -94,8 +113,8 @@ class Travis::Api::App
             github_token           = get_token(endpoint.to_s, values)
             user                   = user_for_github_token(github_token)
             token                  = generate_token(user: user, app_id: 0)
-          rendered_user          = service(:user, user).find_one
+            payload                = params[:state].split(":::", 2)[1]
-          post_message(token: token, user: rendered_user)
+            yield user, token, payload
           else
             values[:state]         = create_state
             endpoint.path          = config.authorize_path
@@ -104,21 +123,16 @@ class Travis::Api::App
           end
         end
 
-      error Faraday::Error::ClientError do
-        halt 401, 'could not resolve github token'
-      end
-
-      private
-
         def create_state
           state = SecureRandom.urlsafe_base64(16)
           redis.sadd('github:states', state)
           redis.expire('github:states', 1800)
+          state << ":::" << params[:redirect_uri] if params[:redirect_uri]
           state
         end
 
         def state_ok?(state)
-          redis.srem('github:states', state) if state
+          redis.srem('github:states', state.split(":::", 1)) if state
         end
 
         def github_to_travis(token, options = {})