One-time passwords (OTPs) are becoming increasingly familiar due to their security benefits over traditional passwords. OTPs can be used instead of or alongside traditional passwords for authentication, ensuring user identity through a communication medium owned by the user, such as a mailbox, phone, or specific app. An OTP service is proposed using two Web APIs: one for creating and sending OTPs via Facebook Messenger or SMS, and another for verifying received OTPs. The OTP service has no user interface and acts as a microservice to generate and verify OTPs. To use this service, Node.js 8.11+ is required, along with a Vonage API account, an application to send HTTP requests, and specific settings in the Vonage API dashboard. The service consists of three components: otpManager, otpRepository, and otpSender, which work together to create, store, and deliver OTPs. The otpManager generates random OTPs, stores them in a file system, and verifies their validity. The otpSender uses the Vonage Dispatch API to send OTPs via Messenger or SMS.