Fix popup authentication flow with proper redirect URL and postMessage communication#15

Copilot wants to merge 3 commits intomasterblackbaud/sky-api-tutorial-auth-code-nodejs:masterfrom

copilot/fix-dc72623b-0d6b-462d-9214-063b53494f3eblackbaud/sky-api-tutorial-auth-code-nodejs:copilot/fix-dc72623b-0d6b-462d-9214-063b53494f3eCopy head branch name to clipboard