How do you stop malicious requests in Azure APIM from repeatedly hitting your rate or quota limits? You have an open facing Azure API Gateway that can be consumed by anyone and you want to protect yourself from the API being spammed by the same IP or the same individual behind multiple IP's.
There are policies one can configure within API Management to:

Limit call rate by subscription
Limit call rate by key
Set usage quota by subscription
Set usage quota by key
Restrict caller IP's

Setting limits by subscription (specific consumers) or key (specific apps) wouldn't work because your API is open to the public, and the last option of restricting caller IP's one-by-one doesn't prevent the issue from happening in the first place.
How do you protect against the same user (IP) repeatedly crushing your rate or quota limits? Additionally, how would you protect against that same user doing this across multiple IP's?
My guess is that this is likely covered in Azure's DDoS Protection Basic but I felt that I couldn't get a concrete answer out of those docs.
You can rate limit or throttle based on the IP: https://docs.microsoft.com/en-us/azure/api-management/api-management-sample-flexible-throttling#ip-address-throttling
Also, Azure DDoS Protection Basic doesn't cover much. It won't know what is normal or not for your application without paying the ~$3,000 per month for the Standard plan.