Blazor OTP Input Made Easy: Secure, Stylish, and Ready for MFA

TL;DR: Learn how to implement a secure and customizable Blazor OTP Input for multi-factor authentication. This guide covers input masking, segmented fields, validation logic, and responsive UI techniques to help developers build robust login workflows in Blazor applications.

Introduction

In today’s security-first development world, multi-factor authentication (MFA) is no longer optional, it’s essential. One-Time Passwords (OTPs) are a cornerstone of secure authentication, adding a critical layer of protection through multi-factor authentication (MFA). Delivered via SMS, email, or authenticator apps, OTPs ensure that only authorized users gain access by requiring a unique, time-sensitive code.

OTPs are a widely adopted method for adding an extra layer of protection to login workflows. However, implementing a secure and user-friendly OTP input can be tricky if you’re building a Blazor application. The Syncfusion Blazor OTP Input component offers a robust solution tailored for this purpose.

This guide walks you through creating a Blazor OTP Input using the Syncfusion Blazor OTP Input component. It focuses on its key features, input types, validation, and styling, along with practical code examples. Explore the Syncfusion Blazor OTP Input demo for a hands-on look.

Why Blazor OTP Input matters for secure authentication?

OTP inputs are vital in MFA workflows, especially in applications that handle sensitive user data. A well-designed OTP input strengthens security and improves the user experience by guiding users through segmented input fields, supporting input masking, and validating entries in real time, just like mobile OTP UIs.

OTPs are temporary codes that expire after a single use or within a short time frame, making them highly effective against unauthorized access. Even if a password is compromised, an OTP adds a critical layer of protection, safeguarding sensitive data in high-risk applications such as banking and e-commerce platforms.

To strike the right balance between security, usability, and aesthetics, developers can leverage modern Blazor components to build OTP inputs that are both functional and intuitive. This is where the Syncfusion Blazor OTP Input stands out, offering built-in features that simplify implementation while enhancing the overall login experience.

Prerequisites

Before we begin, make sure that the following prerequisites are installed:

• Visual Studio 2022
• .NET Core 8.0 and above
• Syncfusion Blazor NuGet package

Setting up the OTP Input field in Blazor

To get started, create a new Blazor Web App using Visual Studio. Then, install the required Syncfusion Blazor packages and configure the style and script reference as outlined in the document.

Exploring the Syncfusion Blazor OTP Input component

The Syncfusion Blazor OTP Input component simplifies OTP entry for MFA scenarios. Key features include:

• Type: Supports number, text, or password inputs, with password mode masking characters for privacy.
• CssClass: It displays success, warning, or error states for immediate user feedback.
• StylingMode: It offers outlined or filled styles with extensive customization.
• Length, placeholder, and separator: It customizes the number of input fields, placeholders, and separators for enhanced UX.

The following sections explore these features in detail, with code examples and styling tips.

Key features

1. Input types: Balancing security and flexibility

The type property supports three modes:

• Number: It restricts input to digits, ideal for numeric OTPs like 123456.
• Text: It allows letters and symbols for complex codes.
• Password: Tt masks input characters, which is perfect for privacy in public settings.

For secure applications, the Password type is recommended. Here’s how to configure it:

<SfOtpInput 
    Type="OtpInputType.Password" 
    Length="6">
</SfOtpInput>

This creates a six-digit OTP input where each character is masked, ideal for public or shared devices. For more details, explore the Type property documentation.

Input Types in Blazor OTP Input component

2. Validation states: Providing instant feedback

The CssClass property allows dynamic validation states like success, warning, or error to guide users. Apply these states as follows:

<SfOtpInput CssClass="e-success"></SfOtpInput>  
<SfOtpInput CssClass="e-error"></SfOtpInput>    
<SfOtpInput CssClass="e-warning"></SfOtpInput>  

You can tie these states to validation logic:

<SfOtpInput CssClass="@otpState"></SfOtpInput>

@code {
    private string otpState = "";

    private void ValidateOtp(string otp)
    {
        if (otp.Length == 6 && IsOtpValid(otp))
            otpState = "e-success";
        else
            otpState = "e-error";
    }

    private bool IsOtpValid(string otp)  
    {  
        // Add your validation logic here. For example:  
        return otp.All(char.IsDigit); // Example: Check if all characters are digits  
    }  
}

This approach provides users with immediate visual feedback, improving the overall authentication experience. For additional customization options, explore the CssClass property documentation.

Validation appearance in the Blazor OTP Input component

3. Styling: Combining security with aesthetics

The Styling Mode property supports Outlined (default) or Filled styles. For a unique look, such as circular input fields, you can apply custom CSS:

<SfOtpInput CssClass="custom-otp"></SfOtpInput>

<style>
    .custom-otp.e-otpinput .e-otp-input-field {
        border-radius: 50%;
        width: 40px;
        height: 40px;
        background-color: #f0f0f0;
        text-align: center;
    }
</style>

This styling creates a sleek, modern appearance that aligns with your app’s branding. You can refer to the Styling Mode documentation for more styling options.

Styling Mode in Blazor OTP Input component

4. Customization: Tailoring the experience

You can adjust the OTP length, add placeholders, or use separators to improve usability:

<SfOtpInput 
    Length="5" 
    Placeholder="*" 
    Separator="-">
</SfOtpInput>

This configuration sets up a five-digit OTP input with asterisks as placeholders and dashes between fields, making the input format clear and user-friendly.

Customization in Blazor OTP Input component

Putting it all together: OTP in a login flow

Let’s build a simple login page with OTP verification. After entering a username and password, the user gets an OTP prompt. Here’s the code:

<h3>Secure Login</h3>

<SfTextBox Placeholder="Username" @bind-Value="username"></SfTextBox>
<SfTextBox Placeholder="Password" Type="InputType.Password" @bind-Value="password"></SfTextBox>

@* Conditional OTP section *@
@if (showOtp)
{
    <div>
        <label>Enter OTP</label>
        <SfOtpInput 
            Type="OtpInputType.Password" 
            Length="6" 
            CssClass="@otpState" 
            @bind-Value="otp">
        </SfOtpInput>
    </div>
}

<button @onclick="HandleLogin">Login</button>

@code {
    private string username = "";
    private string password = "";
    private string otp = "";
    private bool showOtp = false;
    private string otpState = "";

    private void HandleLogin()
    {
        if (!showOtp)
        {
            // Simulate first step: username/password check
            showOtp = true;
        }
        else
        {
            // Simulate OTP validation
            if (otp.Length == 6 && otp == "123456") // Replace with real validation
                otpState = "e-success";
            else
                otpState = "e-error";
        }
    }
}

Login flow in Blazor OTP Input component

This example shows a two-step process: Initial login triggers the OTP field, and submitting the OTP updates the validation state. In a real app, an API is called to verify the OTP on the server side.

Best practices for OTP secure OTP workflows

• Mask inputs: Use Password type to keep OTPs hidden from view, especially on shared or public devices.
• Guide users: Use validation states (success, warning, error) to provide clear and immediate feedback.
• Mobile-friendly: Ensure the layout is responsive, as most users receive OTPs on mobile devices.
• Match length: Set the Length property to match the exact size of your OTP (e.g., 4, 6, or 8 digits).
• Accessibility: Support keyboard navigation and screen readers to make the OTP input accessible to all users.

Conclusion

A secure and well-implemented Syncfusion Blazor OTP Input can significantly improve your app’s authentication flow. By combining segmented fields, input masking, and validation logic, you create a login experience that’s both intuitive and secure. Start integrating OTP today and take your app’s security to the next level.

Explore the Syncfusion Blazor OTP Input documentation and demos to see its full potential. Elevate your Blazor application’s security today!

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This article was originally published at Syncfusion.com.