Request for Reference/Source Code Files for Creating new External System Integration

I'm looking to create a new external system integration for FortiSIEM and I'm seeking guidance on where to find the necessary reference/source code files to get started. I have started with taking reference of this doc but was unable to find the packages/source code files as a reference for building integration from scratch. Can anyone provide me with information on the following:

• Where can I find the reference/source code files for creating a new external system integration?
• Are there any open-source repositories or GitHub projects that I can leverage as a starting point?
• Are there any specific API documentation or developer guides that I should consult to ensure a successful integration?

I'd appreciate any pointers or advice from the community on how to approach this project. Thank you in advance for your help!