When integrating Google Ad Manager (GAM) with an existing middleware system, using a named credential with a custom authentication provider is the most secure and minimally invasive approach. This method enables Salesforce to securely manage authentication credentials, reducing the need for custom code and customizations. The use of named credentials and authentication providers streamlines the integration process, ensuring secure and straightforward access to external systems while adhering to best practices for security and maintainability.References:https://developer.salesforce.com/