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https://docs.microsoft.com/en-us/graph/json-batching
Given we have 1,000 users, we can fetch them in 3 requests, resulting in about ~1.5s * 3 = ~4.5s. Given we have 10,000 users, we should be able to fetch all users' statuses in 25 requests, resulting in about ~1.5s * 25 = ~37.5s if done synchronously. Splitting up the work into goroutines should work nicely since each request is completely independent from the others.
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