Two-factor authentication and OTP sending service

Budget: 200 EUR Deadline: 4 days

Hello! I am ready to create this OTP microservice turnkey. Your stack is exactly my working one: Node.js/TypeScript on Fastify, Redis for storing codes with TTL, adapters for delivery channels.

Here’s how I see the implementation: generating cryptographically secure codes, storing them in Redis with TTL and limits on attempts/resends, endpoints for generate/validate, separate providers for SMS (Twilio), Email (SendGrid), and Telegram (Bot API) behind a unified interface — so that a new channel can be added without rewriting. An isolated internal service, the main application accesses it via an internal REST interface.

A couple of questions to clarify the task: are you planning to use Twilio for SMS or do you already have your own gateway? And do you need limits on input attempts and anti-flood for resending — I usually include this from the start.

As for the timeline — 4 days for a working version with tests. The starting price: I am gathering initial reviews on the platform, so I am offering a good deal — €200. I can show a live demo of our bots right in the chat, so you can assess the level.

Petr Pankov, BotCraft Group

Budget: 500 EUR Deadline: 7 days

Hello. I have extensive experience with Nest.js. I am ready for collaboration.

Budget: 2000 EUR Deadline: 7 days

Hello, I worked on an OTP authentication service for a fintech platform, where we set up the sending of codes via SMS, Email, and Telegram. We reduced the delivery time to 2 seconds ⚡ and decreased the number of unsuccessful logins by 35%.

Tell me, what is the expected time to live (TTL) for the code you plan for confirming financial transactions — and do we need protection against brute-force attacks with an attempt limit?

I suggest we get in touch; I will provide you with free technical consultation and we can create a development plan + I will tell you about my team!

Budget: 150 EUR Deadline: 5 days

Race condition during validation - this is where most OTP services fail. Two requests simultaneously check one code: if invalidation is not atomic, both pass, and a replay attack is open. TTL in Redis alone does not help here - it guarantees expiration but not the "checked-and-removed" binding in one operation. A Lua script (or transaction) is needed that verifies the code and immediately deletes the key so that the second attempt does not find it.

The second point that is often forgotten - a limit on generation. Without it, anyone can send codes in batches, and the bill for Twilio/SendGrid rises unnecessarily. This is essentially a cheap way to drain the budget through your own service.

A couple of questions to avoid guessing. Are all three channels (SMS, Email, Telegram) needed right away in the MVP, or do we start with one or two and connect the rest in the second phase? And where does the rate limit on generation live - on the side of your main application or do we embed it within the service (per-user and per-IP)?

How I see the work in steps: first, a framework on Fastify plus a Redis storage with TTL, then atomic validation through Lua, then delivery providers, and finally limits with basic metrics.

The stack Node/TypeScript/Redis and integrations with Telegram Bot API are what I work with constantly; a recent similar project is accessibilityscanner.top. Therefore, I will be quick. Let's discuss the details in correspondence, and I will also estimate the exact calculation and timelines there.

Budget: 200 EUR Deadline: 1 day

Hello.

I have 13 years of experience in commercial development. I work with Node.js, TypeScript, Redis, Fastify, and Express.

I will implement a separate OTP microservice with support for:

* generating cryptographically secure OTP codes;
* storing codes in Redis with TTL;
* an API for creating, resending, and validating codes;
* protection against brute force;
* sending via SMS, Email, and Telegram;
* integration with Twilio, SendGrid, or other providers;
* Docker configuration and API documentation;
* integration tests of the main logic.

Based on the description, the basic implementation can be completed within a few hours. The deadlines and costs mentioned in the application are approximate — to provide an accurate estimate, it is necessary to clarify the details of the technical specifications, security requirements, list of providers, and the authorization mechanism between the main application and the microservice.

I am ready to start immediately. Expand

Budget: 1200 EUR Deadline: 9 days

├── config/ # Configuration (env, Redis, providers)
├── modules/
│ └── otp/
│ ├── otp.controller.ts # Handling HTTP requests
│ ├── otp.service.ts # Business logic (generation, validation)
│ ├── otp.schema.ts # Input data validation (Fastify/Ajv)
│ └── otp.interface.ts # TypeScript types and interfaces
├── providers/ # Factory and sending providers
│ ├── notification.factory.ts
│ ├── sms.provider.ts
│ ├── email.provider.ts
│ └── telegram.provider.ts
└── app.ts

For generation - crypto

Factory pattern - for scaling channels (SMS, Email, Telegram)

endpoints on Fastify + JSON Schema Validation

The BullMQ queue library works on the same Redis.

Development time estimate - 60-50

Cost estimate - $1200 ($20 per hour)

Contact us

Freelancehunt Expand

Budget: 160 EUR Deadline: 5 days

Ready to develop a reliable and fast OTP microservice in TypeScript / Node.js with high fault tolerance.

What I offer for implementation:

Architecture: Using Fastify — it is more performant than Express and is perfect for lightweight isolated microservices.

Storage and security: Logic on Redis with automatic TTL for codes, as well as built-in Rate Limiting (protection against brute force and frequent repeated requests).

Channel integration: Modular structure for quick setup and independent operation of providers (Twilio — SMS, SendGrid — Email, Telegram Bot API).

Code: Clean, strictly typed code with validation of incoming requests.

I am ready to discuss the exact API format and security requirements in the chat, after which we will finalize the cost and timeline of the project. Expand

Budget: 100 EUR Deadline: 1 day

✋Hello, Ivan Mironets!✋
The most important aspect of developing the current platform is the generation of authentication codes.
There are various methods for this.
It is also important to consider whether the code is for one-time use or if it can be used multiple times.
Next, send the generated code to the user using tools like Twilio, SendGrid, and Resend.
I understand your requirements.
If I understood correctly, I am ready to start immediately.
Thank you.

Budget: 180 EUR Deadline: 3 days

Good day.

In the OTP service, the most important aspect is not just the sending of the code, but the protection against reuse, brute force attacks, and uncontrolled repeated requests. Therefore, I will implement a limited validity period for the code, limits on verification and resending, blocking of used OTPs, and secure storage without recording the codes in plain text.

I will separate the logic for generation, verification, and delivery so that the sending channel can be replaced or expanded without reworking the main authorization. Provider errors and delivery delays will also be handled separately, without exposing the OTP in the logs.

Before delivery, I will check for code expiration, incorrect attempts, reuse, frequent requests, and failures during sending.

The timeframe is up to 3 calendar days, including testing and final verification.

What sending channel is currently being used: SMS, email, or both? Expand

Budget: 500 EUR Deadline: 7 days

Hello, I have extensive experience in development and working with microservices.
Feel free to message me privately.
I will be happy to help you!

Budget: 30 EUR Deadline: 3 days

Good day!

I am a full-stack developer. Stack: Next.js, TypeScript, React, Node.js, Python, PostgreSQL/Prisma.

What I can do for you:
— websites and landing pages from Figma designs, responsive and SEO;
— online stores with integrations: CRM, Nova Poshta, online payments, product feeds;
— Telegram bots and Mini Apps (grammY, aiogram);
— AI integrations: chatbots, RAG agents based on your materials, Claude/OpenAI API;
— automation and parsing in Python (Playwright), working with APIs;
— WebGL / Three.js — interactive 3D scenes and shader animation;
— deployment and server setup: Docker, Nginx, SSL, backups, monitoring.

The code and access will be fully yours after completion. I work through Safe, in phases with clear deadlines and transparent communication. Languages: Ukrainian, Russian, English.

Please write the details of the task — I will provide an estimate and timeline and send examples of my work. Expand

Budget: 400 EUR Deadline: 5 days

Hello!

I am ready to develop a separate OTP microservice with clean architecture and a convenient API for integration with the main application.

What I can implement:

* REST API for generating, verifying, and resending OTP codes;
* storage of codes in Redis with TTL and automatic deletion;
* protection against brute force (rate limiting, limiting the number of attempts, temporary locks);
* support for multiple delivery channels (SMS, Email, Telegram) through a single interface;
* the ability to easily connect new providers (Twilio, SendGrid, SMTP, Telegram Bot API, etc.);
* logging, error handling, and monitoring;
* Docker container for easy deployment.

I develop in TypeScript/Node.js and can use Fastify (preferable due to performance) or Express, depending on your requirements.

In development, I pay special attention to security: the one-time nature of codes, correct operation of TTL, protection against reuse, limiting the number of requests, and ease of future scaling.

I would be happy to discuss the details of the API, the format of integration with the main application, and load requirements.

Best regards,
Dmitry Expand

Budget: 348 EUR Deadline: 5 days

Hello! I have extensive experience in developing microservices using Node.js and TypeScript. I am ready to implement a reliable OTP service, using Redis for managing the TTL of codes and integrating with necessary APIs (Twilio, SendGrid, etc.). I will ensure clean architecture, data validation, and secure token storage. I am ready to discuss the implementation details, feel free to reach out.

Budget: 300 EUR Deadline: 3 days

Good day!

I will create an isolated OTP microservice on Node.js/TypeScript (Fastify) + Redis with TTL.

What will be in the service:

generation of a one-time code + storage in Redis with TTL;
validation (one-time use, attempt limit, expiry);
sending via channels: SMS (Twilio), Email (SendGrid), Telegram;
API for the main application: login / password change / transaction confirmation;
service isolation, structured logs, readiness for deployment.
I am ready to discuss the API details and get started. Expand

Budget: 170 EUR Deadline: 3 days

Hello, I have implemented similar services and can help with the implementation. Stack: Node.js, Ts, express, Redis, BullMQ. Message me privately to discuss timelines and the exact specifications.

Budget: 100 EUR Deadline: 1 day

Good day!
In general, the task is clear. To provide an accurate response regarding the timeline and price, I would like to clarify some questions that arose after analyzing your task.
Please write in private messages – we will discuss the details and your wishes.

Budget: 2000 EUR Deadline: 14 days

Ready to take on your task. I have already had experience in a similar field.