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 {
    implementation 'com.github.hcaptcha:hcaptcha-android-sdk:x.y.z'
}

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

Requirements

Platform	Requirements
Android OS	✅ >= 4.1 (Android API 16)
Wear OS	✖️

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.

Name	Values/Type	Required	Default	Description
siteKey	String	Yes	-	This is your sitekey, this allows you to load challenges. If you need a sitekey, please visit hCaptcha, and sign up to get your sitekey.
size	Enum	No	INVISIBLE	This specifies the "size" of the checkbox component. By default, the checkbox is invisible and the challenge is shown automatically.
orientation	Enum	No	PORTRAIT	This specifies the "orientation" of the challenge.
theme	Enum	No	LIGHT	hCaptcha supports light, dark, and contrast themes.
locale	String (ISO 639-1 code)	No	AUTO	You can enforce a specific language or let hCaptcha auto-detect the local language based on user's device.
resetOnTimeout	Boolean	No	False	(DEPRECATED, use retryPredicate) Automatically reload to fetch new challenge if user does not submit challenge. (Matches iOS SDK behavior.)
retryPredicate	Lambda*	No	-	Automatically trigger a new verification when some error occurs.
jsSrc	String (URL)	No	https://js.hcaptcha.com/1/api.js	See Enterprise docs.
sentry	Boolean	No	True	See Enterprise docs.
rqdata	String	No	-	See Enterprise docs.
apiEndpoint	String (URL)	No	-	(DEPRECATED, use jsSrc) See Enterprise docs.
endpoint	String (URL)	No	-	See Enterprise docs.
reportapi	String (URL)	No	-	See Enterprise docs.
assethost	String (URL)	No	-	See Enterprise docs.
imghost	String (URL)	No	-	See Enterprise docs.
customTheme	Stringified JSON	No	-	See Enterprise docs.
host	String (URL)	No	-	See Enterprise docs.
loading	Boolean	No	True	Show or hide the loading dialog.
hideDialog	Boolean	No	False	To be used in combination with a passive sitekey when no user interaction is required. See Enterprise docs.
tokenExpiration	long	No	120	hCaptcha token expiration timeout (seconds).
diagnosticLog	Boolean	No	False	Emit detailed console logs for debugging
disableHardwareAcceleration	Boolean	No	True	Disable WebView hardware acceleration

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:

Name	Code	Description
NETWORK_ERROR	7	There is no internet connection.
INVALID_DATA	8	Invalid data is not accepted by endpoints.
CHALLENGE_ERROR	9	JS client encountered an error on challenge setup.
INTERNAL_ERROR	10	JS client encountered an internal error.
SESSION_TIMEOUT	15	The challenge expired.
TOKEN_TIMEOUT	16	The token expired.
CHALLENGE_CLOSED	30	The challenge was closed by the user.
RATE_LIMITED	31	Spam detected.
INVALID_CUSTOM_THEME	32	Invalid custom theme.
INSECURE_HTTP_REQUEST_ERROR	33	Insecure resource requested.
ERROR	29	General failure.

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.