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Security, auth & multi-tenancyMediumSDE-2
Your app uses phone number + SMS OTP login. Your SMS bill tripled last month, with lots of OTPs sent to numbers in other countries, and some accounts were brute-forced. How do you redesign the OTP flow?
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PaytmPhonePeSwiggyZepto
Think first
Answer out loud as you would in the room — clarify, give numbers, name the trade-off — then compare with the model answer.
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