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<%@ Page Language="C#" AutoEventWireup="true" %>
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<div class="lang-badge">Java</div>
<h1>Add 2FA to Your Java Application</h1>
<p>A complete guide to integrating Google Authenticator using AuthenticatorAPI.com</p>
</div>
<div class="lang-nav">
<span style="line-height:36px;font-size:13px;font-weight:700;color:#888;">Also available in:</span>
<a href="/integrate-2fa-php.aspx">PHP</a>
<a href="/integrate-2fa-python.aspx">Python</a>
<a href="/integrate-2fa-csharp.aspx">C#</a>
<a href="/integrate-2fa-javascript.aspx">JavaScript</a>
</div>
<p class="lead text-muted">This guide shows how to add Google Authenticator-compatible two-factor authentication to Java applications. We cover both a plain Java utility class and a full Spring Boot integration with Spring Security. No third-party TOTP libraries are required — just Java's standard HTTP client.</p>
<div class="info-box">👉 <strong>Prerequisites:</strong> Java 11+ (for the built-in <code>HttpClient</code>). For Spring Boot, version 3.x is used in examples. A JPA-compatible database for storing user secrets.</div>
<div class="section-heading">Core Utility Class (Plain Java)</div>
<div class="step-block">
<div class="step-num">1</div>
<h3>TotpService.java</h3>
<p>A self-contained service class that wraps all calls to the AuthenticatorAPI. This works in any Java application — Spring, Jakarta EE, or plain Java.</p>
<pre class="code-block"><span class="kw">import</span> java.net.URI;
<span class="kw">import</span> java.net.URLEncoder;
<span class="kw">import</span> java.net.http.HttpClient;
<span class="kw">import</span> java.net.http.HttpRequest;
<span class="kw">import</span> java.net.http.HttpResponse;
<span class="kw">import</span> java.nio.charset.StandardCharsets;
<span class="kw">import</span> java.security.SecureRandom;
<span class="kw">import</span> java.time.Duration;
<span class="kw">public class</span> <span class="dc">TotpService</span> {
<span class="kw">private static final</span> <span class="dc">String</span> BASE32_ALPHABET = <span class="st">"ABCDEFGHIJKLMNOPQRSTUVWXYZ234567"</span>;
<span class="kw">private static final</span> <span class="dc">String</span> API_BASE = <span class="st">"https://www.authenticatorApi.com"</span>;
<span class="kw">private static final</span> <span class="dc">SecureRandom</span> RNG = <span class="kw">new</span> <span class="fn">SecureRandom</span>();
<span class="kw">private final</span> <span class="dc">HttpClient</span> httpClient;
<span class="kw">public</span> <span class="fn">TotpService</span>() {
<span class="kw">this</span>.httpClient = HttpClient.newBuilder()
.connectTimeout(<span class="fn">Duration.ofSeconds</span>(<span class="st">10</span>))
.build();
}
<span class="cm">/** Generates a cryptographically random 32-character Base32 secret. */</span>
<span class="kw">public</span> <span class="dc">String</span> <span class="fn">generateSecret</span>() {
<span class="kw">return</span> <span class="fn">generateSecret</span>(<span class="st">32</span>);
}
<span class="kw">public</span> <span class="dc">String</span> <span class="fn">generateSecret</span>(<span class="kw">int</span> length) {
<span class="dc">StringBuilder</span> sb = <span class="kw">new</span> <span class="fn">StringBuilder</span>(length);
<span class="kw">byte</span>[] bytes = <span class="kw">new byte</span>[length];
RNG.<span class="fn">nextBytes</span>(bytes);
<span class="kw">for</span> (<span class="kw">byte</span> b : bytes) {
sb.<span class="fn">append</span>(BASE32_ALPHABET.charAt((b & <span class="st">0xFF</span>) % <span class="st">32</span>));
}
<span class="kw">return</span> sb.<span class="fn">toString</span>();
}
<span class="cm">/** Returns the HTML img tag for the QR code setup page. */</span>
<span class="kw">public</span> <span class="dc">String</span> <span class="fn">getQrCodeHtml</span>(<span class="dc">String</span> appName, <span class="dc">String</span> userInfo, <span class="dc">String</span> secret)
<span class="kw">throws</span> Exception {
<span class="dc">String</span> url = API_BASE + <span class="st">"/pair.aspx"</span>
+ <span class="st">"?AppName="</span> + <span class="fn">encode</span>(appName)
+ <span class="st">"&AppInfo="</span> + <span class="fn">encode</span>(userInfo)
+ <span class="st">"&SecretCode="</span> + <span class="fn">encode</span>(secret);
<span class="kw">return</span> <span class="fn">get</span>(url);
}
<span class="cm">/** Returns true if the 6-digit pin is valid for the given secret. */</span>
<span class="kw">public boolean</span> <span class="fn">validatePin</span>(<span class="dc">String</span> pin, <span class="dc">String</span> secret) <span class="kw">throws</span> Exception {
<span class="kw">if</span> (!pin.<span class="fn">matches</span>(<span class="st">"\\d{6}"</span>)) <span class="kw">return false</span>;
<span class="dc">String</span> url = API_BASE + <span class="st">"/Validate.aspx"</span>
+ <span class="st">"?Pin="</span> + pin
+ <span class="st">"&SecretCode="</span> + <span class="fn">encode</span>(secret);
<span class="dc">String</span> response = <span class="fn">get</span>(url).<span class="fn">trim</span>();
<span class="kw">return</span> response.<span class="fn">equalsIgnoreCase</span>(<span class="st">"true"</span>);
}
<span class="kw">private</span> <span class="dc">String</span> <span class="fn">get</span>(<span class="dc">String</span> url) <span class="kw">throws</span> Exception {
<span class="dc">HttpRequest</span> request = HttpRequest.newBuilder()
.<span class="fn">uri</span>(<span class="fn">URI.create</span>(url))
.timeout(<span class="fn">Duration.ofSeconds</span>(<span class="st">10</span>))
.<span class="fn">GET</span>()
.build();
<span class="kw">return</span> httpClient
.<span class="fn">send</span>(request, HttpResponse.BodyHandlers.<span class="fn">ofString</span>())
.body();
}
<span class="kw">private</span> <span class="dc">String</span> <span class="fn">encode</span>(<span class="dc">String</span> value) {
<span class="kw">return</span> URLEncoder.<span class="fn">encode</span>(value, StandardCharsets.UTF_8);
}
}</pre>
</div>
<div class="section-heading">Spring Boot Integration</div>
<div class="step-block">
<div class="step-num">2</div>
<h3>Register as a Spring Bean</h3>
<pre class="code-block"><span class="cm">// TotpConfig.java</span>
<span class="kw">import</span> org.springframework.context.annotation.Bean;
<span class="kw">import</span> org.springframework.context.annotation.Configuration;
<span class="dc">@Configuration</span>
<span class="kw">public class</span> <span class="dc">TotpConfig</span> {
<span class="dc">@Bean</span>
<span class="kw">public</span> <span class="dc">TotpService</span> <span class="fn">totpService</span>() {
<span class="kw">return new</span> <span class="fn">TotpService</span>();
}
}</pre>
</div>
<div class="step-block">
<div class="step-num">3</div>
<h3>Spring MVC Controller</h3>
<pre class="code-block"><span class="cm">// TwoFactorController.java</span>
<span class="kw">import</span> org.springframework.stereotype.Controller;
<span class="kw">import</span> org.springframework.ui.Model;
<span class="kw">import</span> org.springframework.web.bind.annotation.*;
<span class="kw">import</span> jakarta.servlet.http.HttpSession;
<span class="dc">@Controller</span>
<span class="dc">@RequestMapping</span>(<span class="st">"/2fa"</span>)
<span class="kw">public class</span> <span class="dc">TwoFactorController</span> {
<span class="kw">private final</span> <span class="dc">TotpService</span> totpService;
<span class="kw">private final</span> <span class="dc">UserService</span> userService;
<span class="kw">public</span> <span class="fn">TwoFactorController</span>(<span class="dc">TotpService</span> totpService, <span class="dc">UserService</span> userService) {
<span class="kw">this</span>.totpService = totpService;
<span class="kw">this</span>.userService = userService;
}
<span class="cm">// GET /2fa/setup — show the QR code</span>
<span class="dc">@GetMapping</span>(<span class="st">"/setup"</span>)
<span class="kw">public</span> <span class="dc">String</span> <span class="fn">setup</span>(<span class="dc">HttpSession</span> session, <span class="dc">Model</span> model) <span class="kw">throws</span> Exception {
<span class="dc">String</span> secret = totpService.<span class="fn">generateSecret</span>();
session.<span class="fn">setAttribute</span>(<span class="st">"pending2faSecret"</span>, secret);
<span class="dc">String</span> username = <span class="cm">/* current principal */</span> <span class="st">""</span>;
model.<span class="fn">addAttribute</span>(<span class="st">"qrHtml"</span>, totpService.<span class="fn">getQrCodeHtml</span>(<span class="st">"MyApp"</span>, username, secret));
model.<span class="fn">addAttribute</span>(<span class="st">"secret"</span>, secret);
<span class="kw">return</span> <span class="st">"2fa/setup"</span>;
}
<span class="cm">// POST /2fa/setup — confirm the user scanned correctly</span>
<span class="dc">@PostMapping</span>(<span class="st">"/setup"</span>)
<span class="kw">public</span> <span class="dc">String</span> <span class="fn">confirmSetup</span>(<span class="dc">@RequestParam</span> <span class="dc">String</span> pin, <span class="dc">HttpSession</span> session, <span class="dc">Model</span> model) <span class="kw">throws</span> Exception {
<span class="dc">String</span> secret = (<span class="dc">String</span>) session.<span class="fn">getAttribute</span>(<span class="st">"pending2faSecret"</span>);
<span class="kw">if</span> (totpService.<span class="fn">validatePin</span>(pin, secret)) {
userService.<span class="fn">saveTotpSecret</span>(<span class="cm">/* userId */</span>, secret);
session.<span class="fn">removeAttribute</span>(<span class="st">"pending2faSecret"</span>);
<span class="kw">return</span> <span class="st">"redirect:/dashboard"</span>;
}
model.<span class="fn">addAttribute</span>(<span class="st">"error"</span>, <span class="st">"Invalid code — please try again."</span>);
<span class="kw">return</span> <span class="st">"2fa/setup"</span>;
}
<span class="cm">// POST /2fa/verify — called during login</span>
<span class="dc">@PostMapping</span>(<span class="st">"/verify"</span>)
<span class="kw">public</span> <span class="dc">String</span> <span class="fn">verify</span>(<span class="dc">@RequestParam</span> <span class="dc">String</span> pin, <span class="dc">HttpSession</span> session, <span class="dc">Model</span> model) <span class="kw">throws</span> Exception {
<span class="dc">String</span> secret = userService.<span class="fn">getDecryptedTotpSecret</span>(<span class="cm">/* userId */</span>);
<span class="kw">if</span> (totpService.<span class="fn">validatePin</span>(pin, secret)) {
session.<span class="fn">setAttribute</span>(<span class="st">"2faVerified"</span>, <span class="kw">true</span>);
<span class="kw">return</span> <span class="st">"redirect:/dashboard"</span>;
}
model.<span class="fn">addAttribute</span>(<span class="st">"error"</span>, <span class="st">"Invalid code — please try again."</span>);
<span class="kw">return</span> <span class="st">"2fa/verify"</span>;
}
}</pre>
</div>
<div class="step-block">
<div class="step-num">4</div>
<h3>Spring Security Filter</h3>
<p>Add a filter that intercepts requests after password authentication and redirects users who haven't yet completed their TOTP check.</p>
<pre class="code-block"><span class="cm">// TwoFactorFilter.java</span>
<span class="kw">import</span> jakarta.servlet.*;
<span class="kw">import</span> jakarta.servlet.http.*;
<span class="kw">import</span> org.springframework.web.filter.OncePerRequestFilter;
<span class="kw">public class</span> <span class="dc">TwoFactorFilter</span> <span class="kw">extends</span> <span class="dc">OncePerRequestFilter</span> {
<span class="kw">private static final</span> <span class="dc">String</span>[] EXEMPT = {<span class="st">"/2fa/"</span>, <span class="st">"/login"</span>, <span class="st">"/logout"</span>, <span class="st">"/css/"</span>, <span class="st">"/js/"</span>};
<span class="dc">@Override</span>
<span class="kw">protected void</span> <span class="fn">doFilterInternal</span>(<span class="dc">HttpServletRequest</span> req, <span class="dc">HttpServletResponse</span> res, <span class="dc">FilterChain</span> chain)
<span class="kw">throws</span> ServletException, IOException {
<span class="dc">HttpSession</span> session = req.<span class="fn">getSession</span>(<span class="kw">false</span>);
<span class="dc">String</span> path = req.<span class="fn">getServletPath</span>();
<span class="kw">boolean</span> isExempt = <span class="kw">false</span>;
<span class="kw">for</span> (<span class="dc">String</span> e : EXEMPT) <span class="kw">if</span> (path.<span class="fn">startsWith</span>(e)) { isExempt = <span class="kw">true</span>; <span class="kw">break</span>; }
<span class="kw">if</span> (!isExempt && session != <span class="kw">null</span>
&& session.<span class="fn">getAttribute</span>(<span class="st">"userId"</span>) != <span class="kw">null</span>
&& !Boolean.TRUE.<span class="fn">equals</span>(session.<span class="fn">getAttribute</span>(<span class="st">"2faVerified"</span>))) {
res.<span class="fn">sendRedirect</span>(<span class="st">"/2fa/verify"</span>);
<span class="kw">return</span>;
}
chain.<span class="fn">doFilter</span>(req, res);
}
}</pre>
</div>
<div class="section-heading">Security Checklist for Java</div>
<ul style="font-size:15px;line-height:2;color:#444;">
<li>✅ Use <code>SecureRandom</code> — never <code>java.util.Random</code></li>
<li>✅ Encrypt secrets with AES-256 before persisting (use JCA or a library like Jasypt)</li>
<li>✅ Use a singleton <code>HttpClient</code> instance — it is thread-safe and connection-pooling aware</li>
<li>✅ Always call the API over HTTPS</li>
<li>✅ Add rate limiting on the verify endpoint (Spring's <code>Bucket4j</code> integration)</li>
<li>✅ Invalidate and regenerate the session after successful 2FA</li>
<li>✅ Provide recovery codes for users who lose their authenticator device</li>
</ul>
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