When would a security engineer need to build an API?

I was reading an AMA with a well established security recruiter and he mentioned probably 5+ times, the engineers who get paid the most, from what he sees, are cloud security engineers who can code (specifically mentioned who can build out API's).

I'm in security and code at my job but it's usually working with API's, manipulating data, building components in AWS but I've never needed to build an API. So this made me wonder, what are some examples of …

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