Enabling third parties to integrate with your core application requires far more than allowing the use of the same API that your front-end already consumes. Access control and cross-domain requests are usually the first spots where problems appear. Based on the experience of integrating OpenProject with Nextcloud we cover the most typical road blocks that product developers should remove. 2023 is different: Like never before publicly funded initiatives strive for replacing big tech’s data hungry cloud services with open-source products. Development teams are busy improving the cross product user experience by developing integrations and hit the same obstacles again and again. This talk tries to create awareness for typical integration developer needs.