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July 30, 2026

🐬 Building High-Fidelity Captive Portals for Flipper Zero

Exploring Captive Portals, Frontend Engineering, UI Replication, and Security Awareness

By Geevarghesekthomas

9 min read

Exploring Captive Portals, Frontend Engineering, UI Replication, and Security Awareness

Cybersecurity becomes much more interesting when we move beyond theory and start building things ourselves.

Recently, I worked on a project called Flipper High-Fidelity Login Portals — a collection of authentication UI experiments designed for Flipper Zero / ESP32-style captive portal environments.

The project combines several areas I enjoy exploring:

🔐 Cybersecurity • 🐬 Flipper Zero • 🌐 Web Security • 🎨 Frontend Development • 📡 Captive Portals • 🧪 Security Research

The objective was not simply to create login pages.

I wanted to understand how modern authentication interfaces work from a frontend perspective, how captive portals behave, and how polished web experiences can be built for environments where normal internet resources may not be available.

⚠️ Ethical Notice: This project is intended strictly for cybersecurity education, security awareness, UI/UX research, and authorized testing in controlled environments. It should never be used to collect information from people without explicit authorization.

🚀 The Idea Behind the Project

Think about connecting to Wi-Fi at an airport, hotel, university, café, or shopping mall.

Normally, the process looks something like this:

📱 Device connects to Wi-Fi
           │
           ▼
📡 Network detected
           │
           ▼
🌐 Connectivity check
           │
           ▼
🔒 Captive portal detected
           │
           ▼
🖥️ Portal displayed
           │
           ▼
✅ User completes portal interaction

Instead of immediately providing unrestricted internet access, the network may display a webpage.

This is commonly known as a captive portal.

Captive portals can be used for legitimate purposes such as:

  • Accepting Wi-Fi terms and conditions
  • Guest authentication
  • Hotel room verification
  • University network access
  • Public hotspot access
  • Enterprise guest networks

I wanted to understand this process beyond the theoretical level.

So I started experimenting with authentication-style interfaces that could operate inside a controlled captive-portal lab.

🎯 The Goal

At first, the project sounds simple:

"Build a login interface."

But once I started working on it, I realized how many small details make a modern authentication experience feel polished.

I had to think about:

Typography
     ↓
Spacing
     ↓
Input Fields
     ↓
Buttons
     ↓
Responsive Layout
     ↓
Animations
     ↓
Form States
     ↓
Mobile Experience

The project therefore became more than a cybersecurity experiment.

It also became an exercise in frontend engineering and UI/UX analysis.

🧩 Authentication UI Designs

The project currently contains four primary authentication UI studies.

I experimented with interfaces inspired by:

Google • Apple • Facebook • Amazon

Each design presented a slightly different frontend challenge.

🔎 Google Login UI

The Google-inspired interface focuses on a clean, minimal, and multi-step authentication experience.

I experimented with:

  • Multi-step UI states
  • Floating input labels
  • Responsive layouts
  • Form validation
  • Smooth transitions
  • Mobile-friendly behavior
  • Lightweight JavaScript interactions

📸 Google Login UI Preview

None

Figure 1 — Google-inspired authentication interface from the Flipper High-Fidelity Login Portals project.

One of the interesting challenges here was reproducing a multi-step interface while keeping everything lightweight.

Instead of displaying every field simultaneously, the UI can move through different visual states.

┌─────────────────────────┐
│                         │
│      Enter Email        │
│                         │
│   user@example.com      │
│                         │
│              NEXT →     │
│                         │
└────────────┬────────────┘
             │
             ▼
┌─────────────────────────┐
│                         │
│     Password Screen     │
│                         │
│       ••••••••••        │
│                         │
│             LOGIN →     │
│                         │
└─────────────────────────┘

This was a useful exercise in managing frontend state using Vanilla JavaScript rather than relying on a large framework.

🍎 Apple Login UI

The Apple-inspired interface presented a different challenge.

The design relies heavily on minimalism.

When an interface contains fewer visible elements, small differences become much more noticeable.

I focused on:

  • Typography
  • Input dimensions
  • Alignment
  • Whitespace
  • Border styling
  • Responsive behavior
  • Minimal visual hierarchy

📸 Apple Login UI Preview

None

Figure 2 — Apple-inspired authentication interface created for the controlled captive-portal lab.

Working on this design showed me how important spacing is.

A few pixels of incorrect padding or an incorrectly sized input field can make a minimal interface feel completely different.

📘 Facebook Login UI

For the Facebook-inspired interface, I focused heavily on responsive behavior and familiar form structure.

📸 Facebook Login UI Preview

None

Figure 3 — Facebook-inspired login UI from the project.

This implementation was particularly useful for testing different screen sizes.

A captive portal might appear inside:

┌─────────────────────┐
│ 📱 Android          │
├─────────────────────┤
│ 📱 iPhone           │
├─────────────────────┤
│ 📟 Tablet           │
├─────────────────────┤
│ 💻 Laptop           │
├─────────────────────┤
│ 🖥️ Desktop          │
└─────────────────────┘

The interface therefore needs to remain usable even when displayed inside a small operating-system captive portal webview.

📦 Amazon Login UI

The Amazon-inspired interface allowed me to experiment with more structured authentication forms.

I focused on areas such as:

  • Form structure
  • Button styling
  • Typography
  • Input states
  • Validation behavior
  • Responsive components
  • Layout consistency

📸 Amazon Login UI Preview

None

Figure 4 — Amazon-inspired authentication interface running in the controlled lab environment.

This implementation reinforced an important frontend lesson:

A recognizable interface is relatively easy to build. A polished interface requires attention to hundreds of small details.

🖼️ UI Showcase

Together, the four interfaces allowed me to experiment with different frontend approaches.

AUTHENTICATION UI
                     │
        ┌────────────┼────────────┐
        │            │            │
        ▼            ▼            ▼
     Google        Apple       Facebook
        │            │            │
   Multi-Step    Minimal UI    Responsive
        │            │            │
        └────────────┼────────────┘
                     │
                     ▼
                   Amazon
                     │
              Structured Forms

Although each interface has a different visual language, they share the same underlying challenge:

How can a modern web experience remain responsive, lightweight, and functional inside a restricted captive-portal environment?

🛠️ Technology Stack

One of my favorite parts of the project is its simplicity.

The interfaces mainly rely on:

┌──────────────────────────────┐
│        FRONTEND STACK        │
├──────────────────────────────┤
│                              │
│  🌐 HTML                     │
│                              │
│  🎨 CSS                      │
│                              │
│  ⚡ Vanilla JavaScript       │
│                              │
│  🖼️ Inline SVG              │
│                              │
└──────────────────────────────┘

No massive frontend framework is required.

That was intentional.

🌐 Why Avoid External Dependencies?

A normal website can load resources from many places across the internet.

For example:

Website
   │
   ├── Fonts
   ├── CDN
   ├── JavaScript Libraries
   ├── External Images
   ├── APIs
   └── Analytics

But captive portal environments can behave differently.

A device may be connected to Wi-Fi while still lacking normal internet connectivity.

That means external resources may fail.

For example:

External font?

❌ Might not load.

Remote image?

❌ Could appear broken.

JavaScript framework hosted on a CDN?

❌ The interface may stop functioning correctly.

This led me to follow a simple principle.

Zero-Network Assets

Where practical, the resources required for the interface should be available locally.

CAPTIVE PORTAL
                │
        ┌───────┼───────┐
        ▼       ▼       ▼
      HTML     CSS   JavaScript
        │       │       │
        └───────┼───────┘
                │
                ▼
           Inline SVG
                │
                ▼
             Browser
                │
                ▼
          Render locally

This makes the frontend much more reliable inside isolated lab environments.

📱 Responsive Design

Responsive design was another important part of the project.

The portal doesn't necessarily open inside a full desktop browser.

Depending on the operating system, it may appear inside a compact captive portal browser.

That means desktop and mobile layouts need to behave differently.

A desktop interface may have:

  • More whitespace
  • Larger components
  • Wider forms
  • Multi-column layouts

A mobile interface needs:

  • Compact spacing
  • Touch-friendly buttons
  • Readable typography
  • Proper input sizing
  • Simplified layouts

This project reinforced an important lesson:

Responsive design isn't simply making everything smaller. It's reorganizing an interface for the available space.

⚡ Multi-Step UI Without a Framework

Another interesting part of the project was creating interactive interface states using Vanilla JavaScript.

A simplified flow might look like:

EMAIL
          │
          ▼
   ┌─────────────┐
   │ Validation  │
   └──────┬──────┘
          │
          ▼
       PASSWORD
          │
          ▼
   ┌─────────────┐
   │ UI Response │
   └─────────────┘

Instead of reloading the entire webpage, JavaScript controls which components are visible.

This gave me more experience with:

  • DOM manipulation
  • Event listeners
  • Form states
  • Input validation
  • UI transitions
  • Frontend state management

And I was able to explore all of this without React or Vue.

🎨 The High-Fidelity Challenge

Recreating a basic form isn't difficult.

Creating an interface that actually feels polished is much harder.

Consider a simple button:

[ Continue ]

Behind that button are many design decisions.

Width
Height
Padding
Font Size
Font Weight
Border Radius
Background
Hover State
Focus State
Alignment
Transition

The same applies to every input field.

And every label.

And every icon.

And every piece of whitespace.

Working on these interfaces gave me a much greater appreciation for professional UI/UX engineering.

📂 Project Structure

I organized the repository so individual implementations can be modified independently.

Flipper-HighFi-Login-Portals/
│
├── Amazon_discord/
├── Amazon_standard/
│
├── Apple_discord/
├── Apple_standard/
│
├── facebook_discord/
├── facebook_standard/
│
├── Google_discord/
├── Google_standard/
│
├── google_local/
│
└── google_server/

This modular structure makes experimentation much easier.

I can modify one implementation without having to completely redesign another.

🔐 The Cybersecurity Lesson

While building the project, one security lesson became especially clear:

Never trust a webpage simply because it looks familiar.

A modern interface can reproduce many familiar visual elements:

✓ Branding
✓ Typography
✓ Buttons
✓ Input Fields
✓ Animations
✓ Responsive Behavior
✓ Form States
✓ Authentication Flow

Visual familiarity does not prove authenticity.

From a security-awareness perspective, users should consider questions such as:

Where did this page come from?

What network am I connected to?

What domain is requesting authentication?

Why am I being asked to authenticate?

Was I expecting this request?

Those questions are far more useful than simply asking:

"Does the website look real?"

🛡️ Defensive Security Perspective

This project can also demonstrate why modern security awareness needs to evolve.

Traditional advice sometimes focuses heavily on poorly designed or obviously suspicious pages.

But visual quality alone isn't a reliable security indicator.

Imagine showing students:

┌─────────────────────┐
│                     │
│   REAL INTERFACE    │
│                     │
└─────────────────────┘
          VS
┌─────────────────────┐
│                     │
│     LAB REPLICA     │
│                     │
└─────────────────────┘

If both look convincing, the lesson becomes much more powerful.

Instead of teaching:

"Look for ugly or badly designed pages."

We can teach:

Verify the origin, domain, network, and context of authentication requests.

That's a much stronger security habit.

🧠 What I Learned

This project improved my understanding across several areas.

🌐 Captive Portal Architecture

I gained a better understanding of how devices detect restricted networks and how captive portal interfaces are presented.

🎨 Frontend Engineering

Recreating polished interfaces improved my HTML and CSS skills.

📱 Responsive Design

Supporting multiple screen sizes forced me to think carefully about layout behavior.

⚡ Vanilla JavaScript

Creating interactive interfaces without a large framework improved my understanding of DOM manipulation and frontend state.

📦 Self-Contained Web Applications

Designing for environments with limited internet connectivity taught me the importance of dependency management.

🔐 Security Awareness

Most importantly, the project reinforced a fundamental security principle:

Visual familiarity should never be treated as proof of authenticity.

⚖️ Ethical Use & Responsible Research

Because this project deals with authentication-style interfaces and captive portals, responsible use is extremely important.

The project is intended for:

✅ Cybersecurity education
✅ Personal security labs
✅ Security awareness demonstrations
✅ Authorized penetration testing
✅ Captive portal research
✅ Frontend development practice
✅ UI/UX experimentation

It should not be used for:

❌ Unauthorized credential collection
❌ Phishing real users
❌ Unauthorized impersonation
❌ Social engineering without consent
❌ Testing networks without permission

Security research should always be performed on systems you own or have explicit authorization to test.

🔬 Why Projects Like This Matter

Cybersecurity isn't learned only through documentation.

There is a major difference between knowing:

"Captive portals exist."

and understanding how the complete system interacts.

DEVICE
                │
                ▼
              Wi-Fi
                │
                ▼
      Connectivity Detection
                │
                ▼
         Captive Portal
                │
                ▼
         Browser / WebView
                │
                ▼
            Frontend
                │
                ▼
        User Interaction

Building projects forces us to understand those connections.

And often, the most valuable learning happens when something doesn't work.

A broken responsive layout.

A missing font.

A captive browser behaving differently.

JavaScript failing.

An SVG rendering incorrectly.

A mobile screen breaking the desktop design.

Finding and fixing those problems creates a deeper understanding than simply reading about the technology.

🚀 What's Next?

There are several areas I'd like to explore further with this project.

FLIPPER HIGH-FIDELITY
                │
                ├── Better mobile compatibility
                │
                ├── More UI experiments
                │
                ├── Performance optimization
                │
                ├── Smaller page sizes
                │
                ├── Better captive-browser support
                │
                └── Security-awareness demos

The project will continue evolving as I experiment with captive portals, frontend engineering, embedded environments, and security research.

🐬 Final Thoughts

Flipper High-Fidelity Login Portals started as a small frontend experiment.

But it quickly became a project connecting several different technologies.

FLIPPER ZERO
                   │
                   ▼
            CAPTIVE PORTALS
                   │
          ┌────────┴────────┐
          │                 │
          ▼                 ▼
     WEB SECURITY      FRONTEND UI
          │                 │
          └────────┬────────┘
                   │
                   ▼
           SECURITY RESEARCH

It helped me better understand how networking, browsers, frontend development, UI/UX, embedded hardware, and cybersecurity can interact inside a single project.

That's one of the things I enjoy most about cybersecurity.

You don't just learn how individual technologies work — you learn how they interact.

🔗 Project

🐙 GitHub Repository

Flipper High-Fidelity Login Portals

https://github.com/geevarghesekthomas84-sys/Flipper-HighFi-Login-Portals

👨‍💻 Author

Geevarghese Thomas

Cybersecurity • Offensive Security • Security Research • Web Development