What Is a Captive Portal Login Using Mobile OTP?

A captive portal is a web page that users see before they can access the internet on a public or managed WiFi network. Instead of allowing open access, the network redirects users to a login page where they must authenticate themselves.

When combined with Mobile OTP (One-Time Password), captive portal login becomes a powerful identity verification method. The user enters their mobile number, receives a time-sensitive OTP via SMS, and gains internet access only after successful verification.

This approach is widely used by ISPs, hotels, airports, cafes, and enterprises across India to ensure that every connected user is authenticated, traceable, and compliant with regulatory requirements.

---

Why Mobile OTP Is the Preferred Login Method for Captive Portals

Traditional username-password login systems come with several challenges — users forget passwords, credentials get shared, and managing accounts at scale is complex. Mobile OTP solves all of these problems in a simple, user-friendly way.

Key Advantages of OTP-Based Captive Portal Login

  • **No password required** — users only need their registered mobile number
  • **Instant authentication** — OTP is delivered within seconds via SMS
  • **Mobile number tied to identity** — ensures traceability as per DOT and TRAI regulations
  • **Reduces support overhead** — no 'forgot password' calls to helpdesk
  • **Works on any device** — no app installation required, browser-based login
  • **Session control** — OTP expiry and session limits prevent unauthorized reuse
💡 In India, mobile numbers are linked to Aadhaar and are considered a reliable form of identity. OTP-based login aligns with KYC norms for ISPs and public WiFi operators.

---

How Captive Portal OTP Login Works — Step by Step

Understanding the technical flow helps ISPs and network administrators deploy this system effectively.

Step 1: User Connects to the WiFi Network

The user selects your WiFi SSID and connects. Their device receives an IP address via DHCP, but internet access is blocked at the gateway level until authentication is complete.

Step 2: Browser Redirect to Captive Portal

When the user opens any website or app, the network intercepts the HTTP/HTTPS request and redirects them to the captive portal login page. This is done using DNS spoofing or transparent proxy techniques configured at the router or NAS (Network Access Server).

Step 3: User Enters Mobile Number

The captive portal displays a clean, branded login interface where the user enters their mobile number. No username or password is needed at this stage.

Step 4: OTP Is Sent via SMS Gateway

The system triggers an SMS to the entered mobile number through an integrated SMS gateway. The OTP is typically 4 to 6 digits and expires within 2 to 5 minutes.

Step 5: User Submits OTP

The user enters the received OTP on the portal. The system validates the OTP against the stored value, checking for correctness and expiry.

Step 6: RADIUS Authentication and Access Grant

Once OTP is validated, the AAA RADIUS server (such as OneRADIUS) grants network access. The RADIUS server assigns the user's session parameters — bandwidth limits, session time, data quota — based on the configured policy.

Step 7: User Is Online

The user is redirected to the original website or a welcome page. Internet access is now fully active within the defined policy limits.

⚠️ Always ensure OTP expiry time is short (under 5 minutes) and implement retry limits to prevent brute force attacks on OTP validation endpoints.

---

Role of RADIUS Server in OTP-Based Captive Portal

The RADIUS server is the backbone of the entire authentication system. It handles:

  • **User session creation and management**
  • **Policy enforcement** — speed limits, data caps, session duration
  • **Accounting** — logging session start, stop, duration, and data usage
  • **Integration with captive portal** — via RADIUS Access-Request and Access-Accept messages
  • **Real-time disconnect** — using RADIUS Change of Authorization (CoA) or Disconnect Messages (DM)

OneRADIUS by ARCR Technologies supports full integration with captive portals and SMS gateways, making OTP-based login deployment straightforward for Indian ISPs.

---

OneRADIUS and Captive Portal OTP Login — Built for Indian ISPs

OneRADIUS is an enterprise-grade AAA RADIUS server software designed specifically for the Indian ISP market. It includes native support for captive portal workflows with mobile OTP authentication.

What OneRADIUS Offers for OTP-Based Captive Portals

  • **SMS gateway integration** — works with popular Indian SMS providers for OTP delivery
  • **Customisable portal templates** — brand the captive portal with your ISP logo and colours
  • **OTP policy configuration** — set OTP length, expiry time, retry limits, and cooldown periods
  • **RADIUS policy binding** — automatically apply bandwidth and session policies post-OTP login
  • **Session reporting** — detailed logs of every OTP login event, session duration, and data consumed
  • **Multi-NAS support** — works with MikroTik, Cisco, Ubiquiti, and other NAS/router platforms
  • **DOT compliance ready** — user login data with mobile number is stored for regulatory reporting
💡 OneRADIUS supports integration with both transactional SMS gateways and WhatsApp OTP delivery for areas with poor SMS delivery rates.

---

Compliance and Security Benefits for ISPs

For ISPs operating in India, OTP-based captive portal login is not just a convenience — it is increasingly becoming a compliance requirement.

Regulatory Alignment

  • **DOT (Department of Telecommunications)** mandates that public WiFi operators must verify user identity before granting access
  • **TRAI** guidelines recommend mobile number-based authentication for accountability
  • **PM-WANI framework** specifically requires OTP-based login for Public Data Office (PDO) WiFi networks

Security Benefits

  • **Prevents anonymous misuse** of public WiFi for illegal activities
  • **OTP expiry** ensures one-time use and prevents credential reuse
  • **Session binding to mobile number** creates an audit trail
  • **Brute-force protection** through retry limits and IP-based rate limiting
⚠️ ISPs must store OTP login logs and session data for a minimum period as required by DOT. Ensure your RADIUS server or BSS system has automated log archival configured.

---

Common Use Cases for OTP Captive Portal Login

ISP Prepaid Hotspots

ISPs deploying public WiFi hotspots in towns, bus stands, railway stations, or shopping areas can use OTP login to allow prepaid access. Users authenticate with OTP, and the system deducts from a prepaid balance or provides a free session of defined duration.

Hotel and Hospitality WiFi

Hotels can offer guests a seamless login experience using their mobile number, eliminating the need to issue WiFi passwords at check-in.

Campus and Co-working Spaces

Managed WiFi providers can give temporary internet access to visitors using OTP, while permanent users have dedicated accounts.

PM-WANI Compliant Public WiFi

ISPs registering as PDOs under the PM-WANI scheme must implement OTP-based captive portal login. OneRADIUS simplifies this with ready-to-use configurations.

---

Technical Architecture Overview

Here is a simplified architecture for an OTP captive portal system powered by OneRADIUS:

  • **WiFi Access Point / Router** — captures unauthenticated users and redirects to portal
  • **Captive Portal Web Server** — serves the login page, handles OTP request and validation
  • **SMS Gateway API** — delivers OTP to user's mobile number
  • **OneRADIUS RADIUS Server** — receives authentication request after OTP validation, enforces policy
  • **Database / BSS** — stores user records, session logs, OTP history
  • **NAS (MikroTik / Cisco / Ubiquiti)** — executes access grant or deny based on RADIUS response

---

Best Practices for Deploying OTP Captive Portal Login

  • **Use HTTPS for the captive portal** — protects OTP in transit and builds user trust
  • **Set strict OTP expiry** — 2 to 3 minutes is ideal for security without frustrating users
  • **Limit OTP retries** — block after 3 to 5 failed attempts and add cooldown timer
  • **Log everything** — store mobile number, timestamp, IP address, session details for compliance
  • **Test SMS delivery** — use a reliable SMS gateway with high delivery rates across Indian telecom circles
  • **Customise the portal UI** — a branded portal improves user trust and reduces abandonment
  • **Monitor session abuse** — use OneRADIUS reporting to detect unusually long or high-data sessions
💡 Consider implementing a 'Resend OTP' button with a 30-second cooldown on the portal UI to handle SMS delay scenarios without allowing abuse.

---

Why Choose OneRADIUS for Your Captive Portal Deployment

OneRADIUS by ARCR Technologies, Hyderabad, is trusted by ISPs across India for its reliability, flexibility, and support. When it comes to OTP-based captive portal deployments, OneRADIUS stands out because:

  • It is purpose-built for **Indian ISP operations** and understands local compliance needs
  • It integrates natively with **MikroTik hotspot and other NAS platforms**
  • It provides **real-time session management** with CoA and disconnect support
  • Its **SMS gateway integrations** are pre-configured for major Indian providers
  • It includes a **web-based admin panel** for easy monitoring and configuration
  • **Dedicated support team** based in Hyderabad understands Indian network environments

---

Conclusion

Captive portal login using mobile OTP is the gold standard for secure, compliant, and user-friendly WiFi access management in India. It eliminates the complexity of password management, meets DOT and TRAI regulatory requirements, and gives ISPs full control over who accesses their network.

With OneRADIUS, deploying an OTP-based captive portal becomes a streamlined, well-supported process — from SMS gateway integration to RADIUS policy enforcement and session reporting.

If you are an ISP looking to modernise your WiFi access management or comply with PM-WANI guidelines, contact ARCR Technologies today and see how OneRADIUS can power your captive portal infrastructure.

Visit oneradius.com to learn more or request a demo.