the traditional way of authenticating a user via Username and password is very much popular in digital world, where as for more security OTP is used, One Time Password is the technique which is two way authentications. This OTP technique can be used as service is cloud to users as One Time Password as service, in OTP as a cloud service some of the cloud service providers will provide this OTP for different cloud users for their online application login and website authentication. Cloud users can register their different web applications in the different cloud service. This will enable for this users access for accounts using OTP verification without maintaining many other passwords and several OTP accounts. In this paper author has given architecture for secure, privacy-friendly and trusted OTP provider and authentication phases are given. The purpose of doing survey of One Time Password as Service is to understand the need on one time password as service for authentication its fundamentals along with drawbacks of different authentication

One Time Password (OTP), Authentication, Cloud, Two-factor Authentication, Multi-factor Authentication, cloud based OTP, cloud-based authentication service

[1] Ieee transactions on information forensics and security, vol. 14, no. 3, march 2019 otpaas one time password as a service emir erdem and mehmet tahir sandkkaya ,member, ieee
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