chore: add oauth flow

app/controllers/github/callbacks_controller.rb

@@ -0,0 +1,71 @@
+class Github::CallbacksController < ApplicationController
+  include Github::IntegrationHelper
+
+  def show
+    @response = oauth_client.auth_code.get_token(
+      params[:code],
+      redirect_uri: "#{base_url}/github/callback"
+    )
+
+    handle_response
+  rescue StandardError => e
+    Rails.logger.error("Github callback error: #{e.message}")
+    redirect_to github_redirect_uri
+  end
+
+  private
+
+  def oauth_client
+    app_id = GlobalConfigService.load('GITHUB_CLIENT_ID', nil)
+    app_secret = GlobalConfigService.load('GITHUB_CLIENT_SECRET', nil)
+
+    OAuth2::Client.new(
+      app_id,
+      app_secret,
+      {
+        site: 'https://github.com',
+        token_url: '/login/oauth/access_token',
+        authorize_url: '/login/oauth/authorize'
+      }
+    )
+  end
+
+  def handle_response
+    hook = account.hooks.new(
+      access_token: parsed_body['access_token'],
+      status: 'enabled',
+      app_id: 'github',
+      settings: {
+        token_type: parsed_body['token_type'],
+        scope: parsed_body['scope']
+      }
+    )
+    hook.save!
+    redirect_to github_redirect_uri
+  rescue StandardError => e
+    Rails.logger.error("Github callback error: #{e.message}")
+    redirect_to github_redirect_uri
+  end
+
+  def account
+    @account ||= Account.find(account_id)
+  end
+
+  def account_id
+    return unless params[:state]
+
+    verify_github_token(params[:state])
+  end
+
+  def github_redirect_uri
+    "#{ENV.fetch('FRONTEND_URL', nil)}/app/accounts/#{account.id}/settings/integrations/github"
+  end
+
+  def parsed_body
+    @parsed_body ||= @response.response.parsed
+  end
+
+  def base_url
+    ENV.fetch('FRONTEND_URL', 'http://localhost:3000')
+  end
+end