Android SDK for hCaptcha

Installation | Requirements | Example App | Usage | Customization | Error Handling | Debugging | FAQ

This SDK provides a wrapper for hCaptcha. It is a drop-in replacement for the SafetyNet reCAPTCHA API. You will need to configure a site key and a secret key from your hCaptcha account in order to use it.

Installation

// Register JitPack Repository inside the root build.gradle file
repositories {
    maven { url 'https://jitpack.io' } 
}
// Add hCaptcha sdk dependency inside the app's build.gradle file
dependencies {
    // For Android View
    implementation 'com.github.hCaptcha.hcaptcha-android-sdk:sdk:x.y.z'
    // For Jetpack Compose
    implementation 'com.github.hCaptcha.hcaptcha-android-sdk:compose-sdk:x.y.z'
}

Note: replace x.y.z with one from Release (e.g. 1.0.0).

Legacy (versions < 5.0)

// Register JitPack Repository inside the root build.gradle file
repositories {
    maven { url 'https://jitpack.io' } 
}
// Add hCaptcha sdk dependency inside the app's build.gradle file
dependencies {
    implementation 'com.github.hcaptcha:hcaptcha-android-sdk:x.y.z'
}

Requirements

Example App

The current repository comes with an example Android application demonstrating 3 different hCaptcha usage patterns.

See the code example below along with the possible customization to enable human verification in your Android application.

Usage

There are multiple ways to run a hCaptcha human verification. See the below snippet for the overall flow.

import com.hcaptcha.sdk.*;
import com.hcaptcha.sdk.tasks.*;

// =================================================
// 1. Initialize a client using the current activity
final HCaptcha hCaptcha = HCaptcha.getClient(this);

// =================================================
// 2. Add the desired listeners
hCaptcha
  .addOnSuccessListener(new OnSuccessListener<HCaptchaTokenResponse>() {
    @Override
    public void onSuccess(HCaptchaTokenResponse response) {
        // Successul verification. The resulting token must be passed to your backend to be validated.
        String userResponseToken = response.getTokenResult();
        Log.d("hCaptcha", "hCaptcha success. Token: " + userResponseToken");
    }
  })
  .addOnFailureListener(new OnFailureListener() {
    @Override
    public void onFailure(HCaptchaException e) {
        // Error handling here: trigger another verification, display a toast, etc.
        Log.d("hCaptcha", "hCaptcha failed: " + e.getMessage() + "(" + e.getStatusCode() + ")");
    }
  })
  .addOnOpenListener(new OnOpenListener() {
    @Override
    public void onOpen() {
        // Usefull for analytics purposes
        Log.d("hCaptcha", "hCaptcha is now visible.");
    }
  });

// =================================================
// 3. Trigger the verification process which may or may not require user input. 
//    It depends on the sitekey difficulty setting and the hCaptcha client configuration.
// 3.1 Optionaly, setup the client to pre-warm the assets.
//     It helps speeding up the actual verification process by having the assets locally already.
hCaptcha.setup(/* args */);
// 3.2 Invoke the actual verification process
//     If "setup(/* args */)" was used, this should be called with empty args.
hCaptcha.verifyWithHCaptcha(/* args */).

// The "args" for setup and verifyWithHCaptcha can be the following:
// 1. The sitekey string.
final String SITE_KEY = "10000000-ffff-ffff-ffff-000000000001";
hCaptcha.setup(SITE_KEY).verifyWithHCaptcha()
// 2. An "HCaptchaConfig" object which allows customization 
//    of the look and feel, the language and more. 
//    See section "Config Params" below.
final HCaptchaConfig hCaptchaConfig = HCaptchaConfig.builder()
        .siteKey("10000000-ffff-ffff-ffff-000000000001")
        .size(HCaptchaSize.NORMAL)
        .theme(HCaptchaTheme.LIGHT)
        .build();
hCaptcha.setup(hCaptchaConfig).verifyWithHCaptcha()
// 3. No params. Sitekey must be configured via `AndroidManifest.xml`.
hCaptcha.setup().verifyWithHCaptcha()
// Set sitekey in AndroidManifest.xml (required only for option 3)
<?xml version="1.0" encoding="utf-8"?>
<application ...>
   <meta-data android:name="com.hcaptcha.sdk.site-key"
              android:value="YOUR_API_SITE_KEY" />
</application>
</manifest>

To remove a specific listener you may use HCaptcha.removeOn[Success|Failure|Open]Listener(listener).

To remove all listeners you may use HCaptcha.removeAllListener().

Note ⚠️: For any sitekey that can show visual challenges, HCaptcha.getClient(Activity) must be called with FragmentActivity instance.

Activity is allowed only when hideDialog=true and sitekey setting is Passive (Enterprise feature).

...
OnSuccessListener<HCaptchaTokenResponse> firstListener = new OnSuccessListener<HCaptchaTokenResponse>() {
    @Override
    public void onSuccess(HCaptchaTokenResponse response) {
        ...
    }
};
hCaptcha.addOnSuccessListener(firstListener).verifyWithHCaptcha();
...
OnSuccessListener<HCaptchaTokenResponse> secondListener = new OnSuccessListener<HCaptchaTokenResponse>() {
    @Override
    public void onSuccess(HCaptchaTokenResponse response) {
        ...
    }
};
hCaptcha.removeOnSuccessListener(firstListener)
    .addOnSuccessListener(secondListener)
    .verifyWithHCaptcha();

For Jetpack Compose

import com.hcaptcha.sdk.HCaptcha
import com.hcaptcha.sdk.HCaptchaException
import com.hcaptcha.sdk.HCaptchaTokenResponse

class HCaptchaActivity : AppCompatActivity() {

    private val hCaptcha = HCaptcha.getClient(this)
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        hCaptcha.setup(BuildConfig.SITE_KEY).verifyWithHCaptcha()
        hCaptcha.addOnSuccessListener { response: HCaptchaTokenResponse ->
            val userResponseToken = response.tokenResult
            val intent = Intent()
            intent.putExtra("captcha", userResponseToken)
            setResult(RESULT_OK, intent)
            finish()
        }.addOnFailureListener { e: HCaptchaException ->
            // Error handling here: trigger another verification, display a toast, etc.
            Log.d("hCaptcha", "hCaptcha failed: " + e.getMessage() + "(" + e.getStatusCode() + ")")
            setResult(RESULT_CANCELED)
            finish()
        }.addOnOpenListener { 
            // Usefull for analytics purposes
            Log.d("hCaptcha", "hCaptcha is now visible.")
        }
    }
}

To fetch token data from activity in @Composable Class:

val intent = Intent(context, HCaptchaActivity::class.java)
                val launcher =
                    rememberLauncherForActivityResult(ActivityResultContracts.StartActivityForResult()) { result ->
                        val data: Intent? = result.data
                        when (result.resultCode) {
                            Activity.RESULT_OK -> {
                                data?.let {
                                    captcha.value = data.extras?.getString("captcha")?: ""
                                }                        
                            }
                            Activity.RESULT_CANCELED -> {
                                Log.d("hCaptcha", "hCaptcha failed")
                            }
                        }
                    }
                SideEffect {
                    launcher.launch(intent)
                }

Memory usage (fragment lifecycle)

We cache the fragment instance inside the SDK to speed up the next HCaptcha.verifyWithHCaptcha calls.

Once you are done with verification, you can call HCaptcha.reset() to release all allocated resources including the strong reference to com.hcaptcha.sdk.HCaptchaDialogFragment.

Note: If you do not call .reset() you will likely see a warning from tools like LeakCanary.

Good to know

1. The listeners (onSuccess, onFailure, onOpen) can be called multiple times in the following cases:
   1. the same client is used to invoke multiple verifications
   2. the config option resetOnTimeout(true) is used which will automatically trigger a new verification when the current token expired. This will result in a new success or error callback.
      • deprecated, please use HCaptchaConfig.retryPredicate
   3. the config option HCaptchaConfig.retryPredicate is used to automatically trigger a new verification when some error occurs. If HCaptchaConfig.retryPredicate returns true, this will result in a new success or error callback.
   4. onFailure with TOKEN_TIMEOUT will be called once the token is expired. To prevent this you can call HCaptchaTokenResponse.markUsed once the token is utilized. Also, you can change expiration timeout with HCaptchaConfigBuilder.tokenExpiration(timeout) (default 2 min.)

Config Params

The following list contains configuration properties to allows customization of the hCaptcha verification flow.

Config Examples

1. Ask the user to complete a challenge without requiring a previous checkbox tap.

final HCaptchaConfig config = HCaptchaConfig.builder()
        .siteKey(YOUR_API_SITE_KEY)
        .size(HCaptchaSize.INVISIBLE)
        .build();

2. Set a specific language, use a dark theme and a compact checkbox.

   final HCaptchaConfig config = HCaptchaConfig.builder()
               .siteKey("YOUR_API_SITE_KEY")
               .locale("ro")
               .size(HCaptchaSize.COMPACT)
               .theme(HCaptchaTheme.DARK)
               .build();

Error handling

In some scenarios in which the human verification process cannot be completed. You can add logic to gracefully handle the errors.

The following is a list of possible error codes:

Retry Failed Verification

You can indicate an automatic verification retry by setting the lambda config HCaptchaConfig.retryPredicate.

One must be careful to not introduce infinite retries and thus blocking the user from error recovering.

Example below will automatically retry in case of CHALLENGE_CLOSED error:

final HCaptchaConfig config = HCaptchaConfig.builder()
        .siteKey("YOUR_API_SITE_KEY")
        .retryPredicate((config, hCaptchaException) -> {
            return hCaptchaException.getHCaptchaError() == HCaptchaError.CHALLENGE_CLOSED;
        })
        .build();
...

Retry predicate serialization

Lambda may implicitly capture variables from its surrounding context. For a lambda to be serializable, all the captured variables must be serializable as well. Failing to meet this requirement can result in runtime errors when attempting to deserialize the lambda.

The retryPredicate is part of HCaptchaConfig that may get persist during application lifecycle. So pay attention to this aspect and make sure that retryPredicate is serializable to avoid android.os.BadParcelableException in run-time.

Debugging Tips

Useful error messages are often rendered on the hCaptcha checkbox. For example, if the sitekey within your config is invalid, you'll see a message there. To quickly debug your local instance using this tool, set .size(HCaptchaSize.NORMAL)

HCaptchaConfigBuilder.diagnosticLog(true) can help to get more detailed logs.

Verify the completed challenge

After retrieving a token, you should pass it to your backend in order to verify the validity of the token by doing a server side check using the hCaptcha secret linked to your sitekey.

FAQ

Can I get a token in a non-UI thread?

No: the SDK depends on WebView, which is a UI component and cannot be instantiated in a non-UI thread.

However, the SDK provides a completely silent (invisible to the end-user) mechanism with hideDialog=true config + "passive" site key (this is an Enterprise feature). But note that the token request still has to be called from the UI thread.

How can I prevent the hCaptcha verification from being canceled when the back button is pressed?

It is possible by specifying HCaptchaConfig.retryPredicate as shown in the following code snippet:

final HCaptchaConfig config = HCaptchaConfig.builder()
        .siteKey("YOUR_API_SITE_KEY")
        .retryPredicate((config, hCaptchaException) -> {
            return hCaptchaException.getHCaptchaError() == HCaptchaError.CHALLENGE_CLOSED;
        })
        .build();

HCaptcha constantly failing with IllegalStateException "Visual Challenge verification require FragmentActivity", how to fix it?

SDK expect to be initialized with FragmentActivity instance in regular scenario.

In case if you use passive siteKey make sure that you called hideDialog(true) on HCaptchaCconfig.builder()

For maintainers

If you plan to contribute to the repo, please see MAINTAINERS.md for detailed build, test, and release instructions.