Tutorial: Integrate GitLab Merge Request approvals with external systems

What this post added

This post introduces and demonstrates the integration of external systems with GitLab Merge Request approvals using the 'External Status Check' feature. It details the deployment of a sample application that receives status check requests from GitLab, stores them, and provides an interface for external users to approve or reject these requests. The post also outlines the steps for configuring this external status check within GitLab and provides debugging tips for the deployed application.