How do I handle authentication headers in cross-origin requests when integrating web services

Handling authentication headers in cross-origin requests (CORS) requires proper server configuration and understanding of browser security policies. When integrating web services, the server must explicitly allow cross-origin requests by setting the Access-Control-Allow-Origin header to the requesting domain (or * for public APIs), and crucially, allow credentials by setting Access-Control-Allow-Credentials: true. To send authentication headers like tokens or cookies, the client (browser) must also set credentials: 'include' or credentials: 'same-origin' in the fetch or XMLHttpRequest call. Additionally, ensure the server includes Access-Control-Allow-Headers with necessary headers like Authorization to permit custom tokens. These best practices are vital if you're building or integrating secure, cross-origin apps. This web development service provides expert support for configuring secure APIs and handling CORS in complex enterprise applications.