The latest articles on DEV Community by Om Kanse (@omkdev). https://dev.to/omkdev https://media2.dev.to/dynamic/image/width=90,height=90,fit=cover,gravity=auto,format=auto/https:%2F%2Fdev-to-uploads.s3.amazonaws.com%2Fuploads%2Fuser%2Fprofile_image%2F3915886%2F7ace00ad-3189-4d2b-9b56-397dc818cf30.png https://dev.to/omkdev en Om Kanse Sun, 31 May 2026 09:20:03 +0000 https://dev.to/omkdev/secure-android-authentication-with-oauth2oidc-pkce-keystore-24i9 https://dev.to/omkdev/secure-android-authentication-with-oauth2oidc-pkce-keystore-24i9 <p>Most Android authentication tutorials stop at “getting the token”.</p> <p>But in real production systems (especially fintech apps), that’s just the beginning.</p> <p>I recently built a secure authentication system using:</p> <p>• OAuth2 Authorization Code Flow with PKCE<br><br> • OpenID Connect (OIDC) via Keycloak<br><br> • AppAuth-Android for browser-based login<br><br> • Android KeyStore with AES-256-GCM encryption<br><br> • Jetpack DataStore for secure persistence<br><br> • Kotlin Flow + MVVM reactive architecture </p> <h2> 🔐 Key Highlights </h2> <ul> <li>Tokens are NEVER stored in plain text </li> <li>Hardware-backed encryption using Android KeyStore </li> <li>PKCE prevents authorization code interception attacks </li> <li>Chrome Custom Tabs instead of insecure WebViews </li> <li>Secure token refresh with race-condition handling </li> <li>Fully reactive authentication state management </li> </ul> <h2> 🧠 Why this matters </h2> <p>Most mobile apps still store tokens in SharedPreferences or insecure storage.</p> <p>That approach is not production-grade for fintech or secure systems.</p> <p>This implementation follows real-world security standards used in production backend + mobile systems.</p> <h2> 🏗 Architecture Overview </h2> <p>The system is built in 3 layers:</p> <h3> 1. UI Layer </h3> <p>Handles login and observes authentication state using MVVM.</p> <h3> 2. Auth Layer (AppAuth-Android) </h3> <p>Handles OAuth2 Authorization Code Flow with PKCE and browser-based login.</p> <h3> 3. Security Layer </h3> <p>Encrypts and stores tokens using:</p> <ul> <li>Android KeyStore</li> <li>AES-256-GCM encryption</li> <li>Secure persistence with DataStore</li> </ul> <h2> ⚡ Key Security Idea: PKCE </h2> <p>PKCE ensures that even if an attacker intercepts the authorization code, they cannot exchange it for tokens without the original <code>code_verifier</code>.</p> <p>This makes OAuth2 safe for mobile public clients.</p> <h2> 🔒 Secure Storage </h2> <p>Tokens are encrypted using:</p> <ul> <li>AES-256-GCM encryption</li> <li>Hardware-backed Android KeyStore</li> <li>Unique IV per encryption</li> </ul> <p>This ensures tokens remain safe even if storage is compromised.</p> <h2> 📌 Final Thoughts </h2> <p>Production authentication is not just “login and get token”.</p> <p>It includes:</p> <ul> <li>Secure transport (OAuth2 + PKCE)</li> <li>Secure storage (KeyStore encryption)</li> <li>Safe architecture (MVVM + reactive flows)</li> <li>Robust lifecycle handling</li> </ul> <h2> 🔗 Full Article + Code </h2> <p>👉 <a href="https://omkanse.hashnode.dev/secure-android-authentication-with-oauth2-oidc-pkce-and-android-keystore" rel="noopener noreferrer">https://omkanse.hashnode.dev/secure-android-authentication-with-oauth2-oidc-pkce-and-android-keystore</a></p> <p>Would love feedback from fellow developers!</p> android oauth security kotlin