Step-by-Step Guide: Implementing OTP API in C#


In an era where online security is of utmost importance, One-Time Password (OTP) authentication has emerged as a reliable method to protect user accounts. By utilizing OTP API in C#—a versatile programming language—developers can effortlessly integrate this powerful security mechanism into their applications. In this article, we will walk you through the process of implementing OTP API in C#, equipping you with the knowledge to enhance the authentication process and fortify your application against unauthorized access.

You can generally take the following actions to use an OTP (One-Time Password) API in C# with ASP.NET:

Open Visual Studio and start a new ASP.NET project.


Install any necessary NuGet packages or libraries for HTTP requests. For this, you can employ a library like HttpClient or RestSharp. Use the Manage NuGet Packages option in Visual Studio or the NuGet Package Manager Console to install the package.


I prefer  as it is made by Microsoft with no 3rd party dependency.

Fill OTP API you wish to utilize and get the API key, endpoint URLs, and any necessary API documentation and credentials.

An example is given above 

Design a new class to handle the integration of the OTP API. This class will include queries to the API functions.

using System;
using System.Net.Http;
using System.Threading.Tasks;

public class OtpApiClient
    private readonly HttpClient _httpClient;
    private readonly string _apiKey;
    private readonly string _apiBaseUrl;

    public OtpApiClient(string apiKey, string apiBaseUrl)
        _httpClient = new HttpClient();
        _apiKey = apiKey;
        _apiBaseUrl = apiBaseUrl;

    public async Task<string> GenerateOtpAsync(string phoneNumber)
        var requestData = new
            phoneNumber = phoneNumber
        var content = new StringContent(
        _httpClient.DefaultRequestHeaders.Add("API-Key", _apiKey);

        var response = await _httpClient.PostAsync(
            _apiBaseUrl + "/generate-otp",

        if (response.IsSuccessStatusCode)
            var responseContent = await response.Content.ReadAsStringAsync();
            var otp = Newtonsoft.Json.JsonConvert
            return otp;
            throw new Exception($"OTP generation failed. StatusCode: {response.StatusCode}");

Once you have created an instance of the OtpApiClient class, you can use the GenerateOtpAsync method. This method takes the necessary parameters required to generate the OTP. By calling this method, you can obtain a unique and temporary password that can be used for secure authentication purposes. you can and use the GenerateOtpAsync method with the necessary parameters in your ASP.NET controller or anywhere you need to generate the OTP. Here, I used a controller.