> ## Documentation Index
> Fetch the complete documentation index at: https://docs.authsignal.com/llms.txt
> Use this file to discover all available pages before exploring further.

# WhatsApp OTP

> Send one-time verification codes via WhatsApp for authentication and for verifying users' phone numbers.

Authsignal SDKs can be used to implement WhatsApp OTP challenges in two scenarios.

1. [Sign-in](#sign-in). Use our Server SDKs to authenticate users with WhatsApp OTP as the 1st factor. This integration only requires a phone number to initiate.
2. [Adaptive MFA](#adaptive-mfa). Use Server SDKs together with Client SDKs to authenticate users with WhatsApp OTP as a secondary factor. This integration requires a user ID to initiate and assumes the user has already been authenticated with a primary factor.

## Portal setup

1. Navigate to [Authenticators](https://portal.authsignal.com/organisations/tenants/authenticators) in the Authsignal Portal and click on **WhatsApp**.
2. Choose and set up a WhatsApp Provider you want to use in the next screen. Then click Connect Account.

<Frame>
  <img src="https://mintcdn.com/authsignal-23/8bvDamO56aVu-Ay2/images/docs/authentication-methods/whatsapp-otp/setup-whatsapp.png?fit=max&auto=format&n=8bvDamO56aVu-Ay2&q=85&s=c87939908abc8b6b7828687d02905cfc" width="2304" height="1286" data-path="images/docs/authentication-methods/whatsapp-otp/setup-whatsapp.png" />
</Frame>

## SDK setup

### Server SDK

Initialize the SDK using your secret key from the [API keys page](https://portal.authsignal.com/organisations/tenants/api) and the [API URL](/sdks/server/setup#regions) for your region.

<CodeGroup>
  ```ts Node.js theme={null}
  import { Authsignal } from "@authsignal/node";

  const authsignal = new Authsignal({
    apiSecretKey: "YOUR_SECRET_KEY",
    apiUrl: "YOUR_API_URL",
  });
  ```

  ```csharp C# theme={null}
  using Authsignal;

  var authsignal = new AuthsignalClient(
      apiSecretKey: "YOUR_SECRET_KEY",
      apiUrl: "YOUR_API_URL"
  );
  ```

  ```java Java theme={null}
  import com.authsignal.AuthsignalClient;

  AuthsignalClient authsignal = new AuthsignalClient(
      "YOUR_SECRET_KEY",
      "YOUR_API_URL"
  );
  ```

  ```ruby Ruby theme={null}
  require 'authsignal'

  Authsignal.setup do |config|
      config.api_secret_key = ENV["YOUR_SECRET_KEY"]
      config.api_url = "YOUR_API_URL"
  end
  ```

  ```python Python theme={null}
  from authsignal.client import AuthsignalClient

  authsignal = AuthsignalClient(
      api_secret_key="YOUR_SECRET_KEY",
      api_url="YOUR_API_URL"
  )
  ```

  ```php PHP theme={null}
  Authsignal::setApiSecretKey("YOUR_SECRET_KEY");
  Authsignal::setApiUrl("YOUR_API_URL");
  ```

  ```go Go theme={null}
  import "github.com/authsignal/authsignalgo/v2/client"

  client := NewAuthsignalClient(
      "YOUR_SECRET_KEY",
      "YOUR_API_URL",
  )
  ```
</CodeGroup>

### Client SDK

Initialize the [Web SDK](/sdks/client/web/setup) or [Mobile SDK](/sdks/client/mobile/setup) using your tenant ID from the [API keys page](https://portal.authsignal.com/organisations/tenants/api) and your [API URL](/sdks/server/setup#regions).

<CodeGroup>
  ```ts Web theme={null}
  import { Authsignal } from "@authsignal/browser";

  const authsignal = new Authsignal({
    tenantId: "YOUR_TENANT_ID",
    baseUrl: "YOUR_API_URL",
  });
  ```

  ```swift iOS theme={null}
  import Authsignal

  let authsignal = Authsignal(
      tenantID: "YOUR_TENANT_ID",
      baseURL: "YOUR_API_URL"
  )
  ```

  ```kotlin Android theme={null}
  import com.authsignal.Authsignal

  val authsignal = Authsignal(
      tenantID = "YOUR_TENANT_ID",
      baseURL = "YOUR_API_URL",
  )
  ```

  ```ts React Native theme={null}
  import { Authsignal } from "react-native-authsignal";

  const authsignal = new Authsignal({
    tenantID: "YOUR_TENANT_ID",
    baseURL: "YOUR_API_URL",
  });
  ```

  ```dart Flutter theme={null}
  import 'package:authsignal_flutter/authsignal_flutter.dart';

  final authsignal = Authsignal(
      "YOUR_TENANT_ID",
      baseURL: "YOUR_API_URL"
  );
  ```
</CodeGroup>

## Sign-in

<Note>**Scenario** - Let users sign-in with WhatsApp OTP as the **1st factor**.</Note>

Our [Server SDKs](/sdks/server) include methods to initiate and verify a WhatsApp OTP challenge for a given phone number.
These methods are well-suited for passwordless sign-in scenarios where you need to authenticate a user based on their phone number.

### 1. Initiate challenge

Call [Initiate Challenge](/sdks/server/challenges#initiate-challenge) to send an OTP to a phone number.

<CodeGroup>
  ```ts Node.js theme={null}
  const request = {
    verificationMethod: "WHATSAPP",
    action: "signInWithWhatsApp",
    phoneNumber: "+64270000000",
  };

  const response = await authsignal.challenge(request);

  const challengeId = response.challengeId;
  ```

  ```csharp C# theme={null}
  var request = new ChallengeRequest(
      VerificationMethod: VerificationMethod.WHATSAPP,
      Action: "signInWithWhatsApp",
      PhoneNumber: "+64270000000"
  );

  var response = await authsignal.challenge(request);

  var challengeId = response.ChallengeId;
  ```

  ```java Java theme={null}
  ChallengeRequest request = new ChallengeRequest();
  request.verificationMethod = VerificationMethodType.WHATSAPP;
  request.action = "signInWithWhatsApp";
  request.phoneNumber = "+64270000000";

  ChallengeResponse response = authsignal.challenge(request).get();

  String challengeId = response.challengeId;
  ```

  ```ruby Ruby theme={null}
  response = Authsignal.challenge(
      verification_method: "WHATSAPP",
      action: "signInWithWhatsApp",
      phone_number: "+64270000000",
  )

  challenge_id = response[:challenge_id]
  ```

  ```go Go theme={null}
  response, err := client.Challenge(
      ChallengeRequest{
          VerificationMethod: "WHATSAPP",
          Action: "signInWithWhatsApp",
          PhoneNumber: "+64270000000",
      },
  )

  challengeId := response.challengeId
  ```
</CodeGroup>

You can choose a value for the [action](/actions-rules/actions/getting-started) here which best describes what the user is doing in your app (e.g. signing in with WhatsApp).
It will be used to track user activity in the Authsignal Portal.

### 2. Verify challenge

Once the user inputs the OTP code, call [Verify Challenge](/sdks/server/challenges#verify-challenge) to verify it.

<CodeGroup>
  ```ts Node.js theme={null}
  const request = {
    challengeId: "3a991a14-690c-492b-a5e5-02b9056a4b7d",
    verificationCode: "123456",
  };

  const response = await authsignal.verify(request);

  const isVerified = response.isVerified;
  ```

  ```csharp C# theme={null}
  var request = new VerifyRequest(
      ChallengeId: "3a991a14-690c-492b-a5e5-02b9056a4b7d",
      VerificationCode: "123456"
  );

  var response = await authsignal.Verify(request);

  var isVerified = response.IsVerified;
  ```

  ```java Java theme={null}
  VerifyRequest request = new VerifyRequest();
  request.challengeId = "3a991a14-690c-492b-a5e5-02b9056a4b7d";
  request.verificationCode = "123456";

  VerifyResponse response = authsignal.verify(request).get();

  boolean isVerified = response.isVerified;
  ```

  ```ruby Ruby theme={null}
  response = Authsignal.verify(
      challenge_id: "3a991a14-690c-492b-a5e5-02b9056a4b7d",
      verification_code: "123456",
  )

  is_verified = response[:is_verified]
  ```

  ```go Go theme={null}
  response, err := client.Verify(
      VerifyRequest{
          ChallengeId: "3a991a14-690c-492b-a5e5-02b9056a4b7d",
          VerificationCode: "123456",
      },
  )

  isVerified := response.IsVerified
  ```
</CodeGroup>

### 3. Claim challenge

Now that the challenge has been verified, you can lookup the user in your IdP or DB based on their phone number.
For passwordless flows with a combined sign-up and sign-in UX, you may need to create the user at this point if no account exists.
Then claim the challenge once you know the primary user ID associated with the phone number.

<CodeGroup>
  ```ts Node.js theme={null}
  const request = {
    challengeId: "3a991a14-690c-492b-a5e5-02b9056a4b7d",
    userId: "dc58c6dc-a1fd-4a4f-8e2f-846636dd4833",
  };

  const response = await authsignal.claimChallenge(request);
  ```

  ```csharp C# theme={null}
  var request = new ClaimChallengeRequest(
      ChallengeId: "3a991a14-690c-492b-a5e5-02b9056a4b7d",
      UserId: "dc58c6dc-a1fd-4a4f-8e2f-846636dd4833"
  );

  var response = await authsignal.ClaimChallenge(request);
  ```

  ```java Java theme={null}
  ClaimChallengeRequest request = new ClaimChallengeRequest();
  request.challengeId = "3a991a14-690c-492b-a5e5-02b9056a4b7d";
  request.userId = "dc58c6dc-a1fd-4a4f-8e2f-846636dd4833";

  ClaimChallengeResponse response = authsignal.claimChallenge(request).get();
  ```

  ```ruby Ruby theme={null}
  response = Authsignal.claim_challenge(
      challenge_id: "3a991a14-690c-492b-a5e5-02b9056a4b7d",
      user_id: "dc58c6dc-a1fd-4a4f-8e2f-846636dd4833",
  )
  ```

  ```go Go theme={null}
  response, err := client.ClaimChallenge(
      ClaimChallengeRequest{
          ChallengeId: "3a991a14-690c-492b-a5e5-02b9056a4b7d",
          UserId: "dc58c6dc-a1fd-4a4f-8e2f-846636dd4833",
      },
  )
  ```
</CodeGroup>

This final step is important because it **attributes activity to the correct user and ensures observability in the Authsignal Portal**.

## Adaptive MFA

<Note>
  **Scenario** - Challenge users with WhatsApp OTP as a **2nd factor** and use rules to decide when
  and where in your app to trigger the challenge.
</Note>

The following steps demonstrate how to implement **adaptive MFA** with WhatsApp OTP - either at sign-in or as step-up authentication when the user performs a sensitive action in your app (e.g. making a payment).

### 1. Track action

Use a [Server SDK](/sdks/server) to track an action in your backend.
This step can apply [rules](/actions-rules/rules/getting-started) to determine if a challenge is required.

<CodeGroup>
  ```ts Node.js theme={null}
  const request = {
    userId: "dc58c6dc-a1fd-4a4f-8e2f-846636dd4833",
    action: "signIn",
    attributes: {
      phoneNumber: "+64270000000",
    },
  };

  const response = await authsignal.track(request);

  if (response.state === "CHALLENGE_REQUIRED") {
    // Obtain token to present challenge
    const token = response.token;
  }
  ```

  ```csharp C# theme={null}
  var request = new TrackRequest(
      UserId: "dc58c6dc-a1fd-4a4f-8e2f-846636dd4833",
      Action: "signIn",
      Attributes: new TrackAttributes(
          PhoneNumber: "+64270000000"
      )
  );

  var response = await authsignal.Track(request);

  if (response.State == UserActionState.CHALLENGE_REQUIRED)
  {
      // Obtain token to present challenge
      var token = response.Token;
  }
  ```

  ```java Java theme={null}
  TrackRequest request = new TrackRequest();
  request.userId = "dc58c6dc-a1fd-4a4f-8e2f-846636dd4833";
  request.action = "signIn";
  request.attributes = new TrackAttributes();
  request.attributes.phoneNumber = "+64270000000";

  TrackResponse response = authsignal.track(request).get();

  if (response.state.equals(UserActionState.CHALLENGE_REQUIRED)) {
      // Obtain token to present challenge
      String token = response.token;
  }
  ```

  ```ruby Ruby theme={null}
  response = Authsignal.track({
    user_id: 'dc58c6dc-a1fd-4a4f-8e2f-846636dd4833',
    action: 'signIn',
    attributes: {
      phone_number: '+64270000000'
    }
  })

  case response[:state]
  when "CHALLENGE_REQUIRED"
    # Obtain token to present challenge
    token = response[:token]
  end
  ```

  ```python Python theme={null}
  response = authsignal.track(
      user_id="dc58c6dc-a1fd-4a4f-8e2f-846636dd4833",
      action="signIn",
      attributes={
          "phoneNumber": "+64270000000"
      }
  )

  if response["state"] == "CHALLENGE_REQUIRED":
      # Obtain token to present challenge
      token = response["token"]
  ```

  ```php PHP theme={null}
  $response = $authsignal->track([
      'userId' => 'dc58c6dc-a1fd-4a4f-8e2f-846636dd4833',
      'action' => 'signIn',
      'attributes' => [
          'phoneNumber' => '+64270000000'
      ]
  ]);

  switch ($response['state']) {
      case 'CHALLENGE_REQUIRED':
          // Obtain token to present challenge
          $token = $response['token'];
  }
  ```

  ```go Go theme={null}
  response, err := client.Track(
      TrackRequest{
          UserId: "dc58c6dc-a1fd-4a4f-8e2f-846636dd4833",
          Action: "signIn",
          Attributes: &TrackAttributes{
              PhoneNumber: "+64270000000",
          },
      },
  )

  switch response.State {
  case "CHALLENGE_REQUIRED":
      // Obtain token to present challenge
      token := response.Token
  }
  ```
</CodeGroup>

You can choose a value for the [action](/actions-rules/actions/getting-started) here which best describes what the user is doing in your app (e.g. `signIn` or `createPayment`).
Each action can have its own set of rules.
To learn more about using rules and handling different action states refer to our documentation on [actions](/actions-rules/actions/getting-started) and [rules](/actions-rules/rules/getting-started).

### 2. Present challenge

If the action state is `CHALLENGE_REQUIRED` then you can present a WhatsApp OTP challenge using the [Web SDK](/sdks/client/web/setup) or [Mobile SDK](/sdks/client/mobile/setup).

<Tabs>
  <Tab title="Custom UI">
    <CodeGroup>
      ```ts Web theme={null}
      // Set token from the track response
      authsignal.setToken("eyJhbGciOiJ...");

      // Send the user a WhatsApp OTP code
      // You can call this multiple times via a 'resend' button
      await authsignal.whatsapp.challenge();

      // Verify the inputted code matches the original code
      const response = await authsignal.whatsapp.verify({ code: "123456" });

      // Obtain a new token
      const token = response.token;
      ```

      ```swift iOS theme={null}
      // Set token from the track response
      authsignal.setToken("eyJhbGciOiJ...")

      // Send the user a WhatsApp OTP code
      // You can call this multiple times via a 'resend' button
      await authsignal.whatsapp.challenge()

      // Verify the inputted code matches the original code
      let response = await authsignal.whatsapp.verify(code: "123456")

      // Obtain a new token
      let token = response.token
      ```

      ```kotlin Android theme={null}
      // Set token from the track response
      authsignal.setToken("eyJhbGciOiJ...")

      // Send the user a WhatsApp OTP code
      // You can call this multiple times via a 'resend' button
      authsignal.whatsapp.challenge()

      // Verify the inputted code matches the original code
      val response = authsignal.whatsapp.verify(code = "123456")

      // Obtain a new token
      val token = response.token
      ```

      ```ts React Native theme={null}
      // Set token from the track response
      await authsignal.setToken("eyJhbGciOiJ...");

      // Send the user a WhatsApp OTP code
      // You can call this multiple times via a 'resend' button
      await authsignal.whatsapp.challenge();

      // Verify the inputted code matches the original code
      const response = await authsignal.whatsapp.verify({ code: "123456" });

      // Obtain a new token
      const token = response.token;
      ```

      ```dart Flutter theme={null}
      // Set token from the track response
      await authsignal.setToken("eyJhbGciOiJ...");

      // Send the user a WhatsApp OTP code
      // You can call this multiple times via a 'resend' button
      await authsignal.whatsapp.challenge();

      // Verify the inputted code matches the original code
      final response = await authsignal.whatsapp.verify(code: "123456");

      // Obtain a new token
      final token = response.token;
      ```
    </CodeGroup>
  </Tab>

  <Tab title="Pre-built UI">
    <CodeGroup>
      ```js Web theme={null}
      // Launch the pre-built UI with the URL from the track response
      const result = await authsignal.launch(url);

      // Obtain a token to validate in the next step
      if (result.token) {
        const token = result.token;
      }
      ```
    </CodeGroup>
  </Tab>
</Tabs>

### 3. Validate action

Use the new token obtained from the client SDK to validate the action on your backend.

<CodeGroup>
  ```ts Node.js theme={null}
  const response = await authsignal.validateChallenge({
    action: "signIn",
    token: "eyJhbGciOiJIUzI....",
  });

  if (response.state === "CHALLENGE_SUCCEEDED") {
    // User completed challenge successfully
  }
  ```

  ```csharp C# theme={null}
  var request = new ValidateChallengeRequest(
      Action: "signIn",
      Token: "eyJhbGciOiJIUzI...."
  );

  var response = await authsignal.ValidateChallenge(request);

  if (response.State == UserActionState.CHALLENGE_SUCCEEDED) {
      // User completed challenge successfully
  }
  ```

  ```java Java theme={null}
  ValidateChallengeRequest request = new ValidateChallengeRequest();
  request.action = "signIn";
  request.token = "eyJhbGciOiJIUzI....";

  ValidateChallengeResponse response = authsignal.validateChallenge(request).get();

  if (response.state == UserActionState.CHALLENGE_SUCCEEDED) {
     // User completed challenge successfully
  }
  ```

  ```ruby Ruby theme={null}
  response = Authsignal.validate_challenge(action: "signIn", token: "eyJhbGciOiJIUzI....")

  if response[:state] == "CHALLENGE_SUCCEEDED"
    # User completed challenge successfully
  end
  ```

  ```python Python theme={null}
  response = authsignal.validate_challenge(action="signIn", token="eyJhbGciOiJIUzI....")

  if response["state"] == "CHALLENGE_SUCCEEDED":
      # User completed challenge successfully
  ```

  ```php PHP theme={null}
  $response = Authsignal::validateChallenge(action: "signIn", token: "eyJhbGciOiJIUzI....");

  if ($response["state"] === "CHALLENGE_SUCCEEDED") {
      # User completed challenge successfully
  }
  ```

  ```go Go theme={null}
  response, err := client.ValidateChallenge(
      ValidateChallengeRequest{
          Action: "signIn",
          Token: "eyJhbGciOiJ...",
      },
  )

  if response.State == "CHALLENGE_SUCCEEDED" {
      // User completed challenge successfully
  }
  ```
</CodeGroup>

If the action state shows that the WhatsApp OTP challenge was completed successfully, you can let the user proceed with the action.

## Enrollment

<Note>
  **Scenario** - Enroll users in WhatsApp OTP while they’re authenticated so it can be used later as
  a method for adaptive MFA.
</Note>

To use WhatsApp OTP for adaptive MFA, users must be **enrolled** with WhatsApp OTP as an authentication method.
This means their phone number has previously been verified and can be trusted.

The following steps demonstrate how to implement an enrollment flow using a [Server SDK](/sdks/server/overview).

### 1. Initiate challenge

Call [Initiate Challenge](/sdks/server/challenges#initiate-challenge) to send an OTP to a phone number.

<CodeGroup>
  ```ts Node.js theme={null}
  const request = {
    verificationMethod: "WHATSAPP",
    action: "enrollWhatsApp",
    phoneNumber: "+64270000000",
    userId: "dc58c6dc-a1fd-4a4f-8e2f-846636dd4833",
    scope: "add:authenticators",
  };

  const response = await authsignal.challenge(request);

  const challengeId = response.challengeId;
  ```

  ```csharp C# theme={null}
  var request = new ChallengeRequest(
      VerificationMethod: VerificationMethod.WHATSAPP,
      Action: "enrollWhatsApp",
      PhoneNumber: "+64270000000",
      UserId: "dc58c6dc-a1fd-4a4f-8e2f-846636dd4833",
      Scope: "add:authenticators",
  );

  var response = await authsignal.challenge(request);

  var challengeId = response.ChallengeId;
  ```

  ```java Java theme={null}
  ChallengeRequest request = new ChallengeRequest();
  request.verificationMethod = VerificationMethodType.WHATSAPP;
  request.action = "enrollWhatsApp";
  request.phoneNumber = "+64270000000";
  request.userId = "dc58c6dc-a1fd-4a4f-8e2f-846636dd4833";
  request.scope = "add:authenticators";

  ChallengeResponse response = authsignal.challenge(request).get();

  String challengeId = response.challengeId;
  ```

  ```ruby Ruby theme={null}
  response = Authsignal.challenge(
      verification_method: "WHATSAPP",
      action: "enrollWhatsApp",
      phone_number: "+64270000000",
      user_id: "dc58c6dc-a1fd-4a4f-8e2f-846636dd4833",
      scope: "add:authenticators",
  )

  challenge_id = response[:challenge_id]
  ```

  ```go Go theme={null}
  response, err := client.Challenge(
      ChallengeRequest{
          VerificationMethod: "WHATSAPP",
          Action: "enrollWhatsApp",
          PhoneNumber: "+64270000000",
          UserId: "dc58c6dc-a1fd-4a4f-8e2f-846636dd4833",
          Scope: "add:authenticators",
      },
  )

  challengeId := response.challengeId
  ```
</CodeGroup>

The **add:authenticators** scope is required to enroll a new WhatsApp authenticator for an existing user.
This scope should only be used **when the user is in an already authenticated state**.
For more information on using scopes safely refer to our documentation on [authenticator binding](/advanced-usage/authenticator-binding).

### 2. Verify challenge

Once the user inputs the OTP code, call [Verify Challenge](/sdks/server/challenges#verify-challenge) to verify it.

<CodeGroup>
  ```ts Node.js theme={null}
  const request = {
    challengeId: "3a991a14-690c-492b-a5e5-02b9056a4b7d",
    verificationCode: "123456",
  };

  const response = await authsignal.verify(request);

  const isVerified = response.isVerified;
  ```

  ```csharp C# theme={null}
  var request = new VerifyRequest(
      ChallengeId: "3a991a14-690c-492b-a5e5-02b9056a4b7d",
      VerificationCode: "123456"
  );

  var response = await authsignal.Verify(request);

  var isVerified = response.IsVerified;
  ```

  ```java Java theme={null}
  VerifyRequest request = new VerifyRequest();
  request.challengeId = "3a991a14-690c-492b-a5e5-02b9056a4b7d";
  request.verificationCode = "123456";

  VerifyResponse response = authsignal.verify(request).get();

  boolean isVerified = response.isVerified;
  ```

  ```ruby Ruby theme={null}
  response = Authsignal.verify(
      challenge_id: "3a991a14-690c-492b-a5e5-02b9056a4b7d",
      verification_code: "123456",
  )

  is_verified = response[:is_verified]
  ```

  ```go Go theme={null}
  response, err := client.Verify(
      VerifyRequest{
          ChallengeId: "3a991a14-690c-492b-a5e5-02b9056a4b7d",
          VerificationCode: "123456",
      },
  )

  isVerified := response.IsVerified
  ```
</CodeGroup>

## Update phone number

<Note>
  **Scenario** - Let users update their phone number while they’re authenticated, completing an OTP
  challenge to verify the new number.
</Note>

The following steps demonstrate how to implement an update phone number flow using a [Server SDK](/sdks/server/overview).

### 1. Initiate challenge

Call [Initiate Challenge](/sdks/server/challenges#initiate-challenge) to send an OTP to the user's new phone number.

<CodeGroup>
  ```ts Node.js theme={null}
  const request = {
    verificationMethod: "WHATSAPP",
    action: "updatePhoneNumber",
    phoneNumber: "+64270000000",
    userId: "dc58c6dc-a1fd-4a4f-8e2f-846636dd4833",
    scope: "update:authenticators",
  };

  const response = await authsignal.challenge(request);

  const challengeId = response.challengeId;
  ```

  ```csharp C# theme={null}
  var request = new ChallengeRequest(
      VerificationMethod: VerificationMethod.WHATSAPP,
      Action: "updatePhoneNumber",
      PhoneNumber: "+64270000000",
      UserId: "dc58c6dc-a1fd-4a4f-8e2f-846636dd4833",
      Scope: "update:authenticators",
  );

  var response = await authsignal.challenge(request);

  var challengeId = response.ChallengeId;
  ```

  ```java Java theme={null}
  ChallengeRequest request = new ChallengeRequest();
  request.verificationMethod = VerificationMethodType.WHATSAPP;
  request.action = "updatePhoneNumber";
  request.phoneNumber = "+64270000000";
  request.userId = "dc58c6dc-a1fd-4a4f-8e2f-846636dd4833";
  request.scope = "update:authenticators";

  ChallengeResponse response = authsignal.challenge(request).get();

  String challengeId = response.challengeId;
  ```

  ```ruby Ruby theme={null}
  response = Authsignal.challenge(
      verification_method: "WHATSAPP",
      action: "updatePhoneNumber",
      phone_number: "+64270000000",
      user_id: "dc58c6dc-a1fd-4a4f-8e2f-846636dd4833",
      scope: "update:authenticators",
  )

  challenge_id = response[:challenge_id]
  ```

  ```go Go theme={null}
  response, err := client.Challenge(
      ChallengeRequest{
          VerificationMethod: "WHATSAPP",
          Action: "updatePhoneNumber",
          PhoneNumber: "+64270000000",
          UserId: "dc58c6dc-a1fd-4a4f-8e2f-846636dd4833",
          Scope: "update:authenticators",
      },
  )

  challengeId := response.challengeId
  ```
</CodeGroup>

The **update:authenticators** scope is required to update a user's existing WhatsApp authenticator to change the phone number.
This scope should only be used **when the user is in an already authenticated state**.
For more information on using scopes safely refer to our documentation on [authenticator binding](/advanced-usage/authenticator-binding).

### 2. Verify challenge

Once the user inputs the OTP code, call [Verify Challenge](/sdks/server/challenges#verify-challenge) to verify it.

<CodeGroup>
  ```ts Node.js theme={null}
  const request = {
    challengeId: "3a991a14-690c-492b-a5e5-02b9056a4b7d",
    verificationCode: "123456",
  };

  const response = await authsignal.verify(request);

  const isVerified = response.isVerified;
  ```

  ```csharp C# theme={null}
  var request = new VerifyRequest(
      ChallengeId: "3a991a14-690c-492b-a5e5-02b9056a4b7d",
      VerificationCode: "123456"
  );

  var response = await authsignal.Verify(request);

  var isVerified = response.IsVerified;
  ```

  ```java Java theme={null}
  VerifyRequest request = new VerifyRequest();
  request.challengeId = "3a991a14-690c-492b-a5e5-02b9056a4b7d";
  request.verificationCode = "123456";

  VerifyResponse response = authsignal.verify(request).get();

  boolean isVerified = response.isVerified;
  ```

  ```ruby Ruby theme={null}
  response = Authsignal.verify(
      challenge_id: "3a991a14-690c-492b-a5e5-02b9056a4b7d",
      verification_code: "123456",
  )

  is_verified = response[:is_verified]
  ```

  ```go Go theme={null}
  response, err := client.Verify(
      VerifyRequest{
          ChallengeId: "3a991a14-690c-492b-a5e5-02b9056a4b7d",
          VerificationCode: "123456",
      },
  )

  isVerified := response.IsVerified
  ```
</CodeGroup>

## Verified phone numbers

<Note>
  **Scenario** - Enroll or update a WhatsApp authenticator for a user when you've already verified
  their phone number in another system, so it can be used later as a method for adaptive MFA.
</Note>

In some cases you may have already verified a user's phone number using another system.
This means the user can be enrolled without having to complete a WhatsApp OTP challenge.

<CodeGroup>
  ```ts Node.js theme={null}
  const request = {
    userId: "dc58c6dc-a1fd-4a4f-8e2f-846636dd4833",
    attributes: {
      verificationMethod: "WHATSAPP",
      phoneNumber: "+64270000000",
    },
  };

  const response = authsignal.enrollVerifiedAuthenticator(request);
  ```

  ```csharp C# theme={null}
  var request = new EnrollVerifiedAuthenticatorRequest(
      UserId: "dc58c6dc-a1fd-4a4f-8e2f-846636dd4833",
      Attributes: new EnrollVerifiedAuthenticatorAttributes(
          VerificationMethod: VerificationMethod.WHATSAPP,
          PhoneNumber: "+64270000000"
      )
  );

  var response = await authsignal.EnrollVerifiedAuthenticator(request);
  ```

  ```java Java theme={null}
  EnrollVerifiedAuthenticatorRequest request = new EnrollVerifiedAuthenticatorRequest();
  request.userId = "dc58c6dc-a1fd-4a4f-8e2f-846636dd4833";
  request.attributes = new EnrollVerifiedAuthenticatorAttributes();
  request.attributes.verificationMethod = VerificationMethodType.WHATSAPP;
  request.attributes.phoneNumber = "+64270000000";

  authsignal.enrollVerifiedAuthenticator(request).get();
  ```

  ```ruby Ruby theme={null}
  Authsignal.enroll_verified_authenticator(
      user_id: "dc58c6dc-a1fd-4a4f-8e2f-846636dd4833",
      attributes:{
          verification_method: "WHATSAPP",
          phone_number: "+64270000000"
      }
  )
  ```

  ```python Python theme={null}
  response = authsignal.enroll_verified_authenticator(
      user_id="dc58c6dc-a1fd-4a4f-8e2f-846636dd4833",
      attributes={
          "verificationMethod": "WHATSAPP",
          "phoneNumber": "+64270000000"
      }
  )
  ```

  ```php PHP theme={null}
  $response = Authsignal::enrollVerifiedAuthenticator([
      'userId' => "dc58c6dc-a1fd-4a4f-8e2f-846636dd4833",
      'attributes' => [
          "verificationMethod" => "WHATSAPP",
          "phoneNumber" => "+64270000000"
      ]
  ]);
  ```

  ```go Go theme={null}
  response, err := client.EnrollVerifiedAuthenticator(
      EnrollVerifiedAuthenticatorRequest{
          UserId: "dc58c6dc-a1fd-4a4f-8e2f-846636dd4833",
          Attributes: &EnrollVerifiedAuthenticatorAttributes{
              VerificationMethod: "WHATSAPP",
              PhoneNumber: "+64270000000",
          },
      },
  )

  ```
</CodeGroup>

This same call can also be used to **update** a verified phone number to a new value which has also been verified externally.

## Next steps

* [Pre-built UI](/implementation-options/prebuilt-ui/overview) - Rapidly deploy WhatsApp OTP challenges using our pre-built UI
* [Web SDK](/sdks/client/web/setup) - Implement WhatsApp OTP challenges while building your own UI
* [Mobile SDK](/sdks/client/mobile/setup) - Implement WhatsApp OTP challenges in native mobile apps
* [Adaptive MFA](/actions-rules/rules/adaptive-mfa) - Set up smart rules to trigger authentication based on risk
* [Passkeys](/authentication-methods/passkey/web-sdk) - Offer the most secure and user-friendly passwordless authentication