postMessage Authentication

Overview

The postMessage API provides secure, real-time cross-origin communication between your parent window and the embedded webview. This is the recommended method for handling sensitive authentication data.

How It Works

Generate Custom Token

Your backend calls the Doshi API to generate a custom token

Webview Sends PING

The embedded webview sends a PING message to signal it’s ready

Parent Receives PING

Parent window listens for the PING and prepares authentication data

Parent Sends AUTH

Parent sends the custom token and user data back to the webview

Webview Processes AUTH

Webview receives and processes the authentication, handling 2FA if needed

TypeScript Interfaces

interface AuthData {
  token: string;              // Required - custom token from API
  email?: string;             // Optional - user's email
  segment?: string;           // Optional - for multiple paths
  branchId?: string;          // Optional - branch identifier
  
  // 2FA Parameters (optional, required when is2FaEnabled is true)
  is2FaEnabled?: boolean;     // Enable 2FA flow in iframe
  dob?: string;               // Date of birth (YYYY-MM-DD)
  organizationId?: string;    // Organization ID
  partnerUserId?: string;     // Partner user ID
  firstName?: string;         // First name
  lastName?: string;          // Last name
}

interface WebviewMessage {
  type: string;
  [key: string]: any;
}

React Implementation

Complete Example with API Call

import React, { useEffect, useState } from "react";

interface AuthData {
  token: string;
  email?: string;
  segment?: string;
  branchId?: string;
  is2FaEnabled?: boolean;
  dob?: string;
  organizationId?: string;
  partnerUserId?: string;
  firstName?: string;
  lastName?: string;
}

interface WebviewMessage {
  type: string;
  [key: string]: any;
}

interface Props {
  userEmail: string;
  segment?: string;
  branchId?: string;
  // 2FA props
  is2FaEnabled?: boolean;
  dob?: string;
  organizationId?: string;
  partnerUserId?: string;
  firstName?: string;
  lastName?: string;
}

const WebviewComponent: React.FC<Props> = ({ 
  userEmail,
  segment,
  branchId,
  is2FaEnabled = false,
  dob,
  organizationId,
  partnerUserId,
  firstName,
  lastName
}) => {
  const [authToken, setAuthToken] = useState<string | null>(null);
  const [isLoading, setIsLoading] = useState(true);
  const [error, setError] = useState<string | null>(null);

  // Step 1: Get nonce token from your backend
  useEffect(() => {
    async function fetchToken() {
      try {
        // Call YOUR backend which securely calls Doshi API
        const response = await fetch('/api/generate-doshi-token', {
          method: 'POST',
          headers: {
            'Content-Type': 'application/json'
          },
          body: JSON.stringify({
            email: userEmail,
            branchId
          })
        });

        if (!response.ok) {
          throw new Error('Failed to generate token');
        }

        const data = await response.json();
        setAuthToken(data.token);
      } catch (error) {
        console.error('Failed to fetch auth token:', error);
        setError('Authentication failed. Please try again.');
      } finally {
        setIsLoading(false);
      }
    }

    fetchToken();
  }, [userEmail, branchId]);

  // Step 2: Setup postMessage listener
  useEffect(() => {
    if (!authToken) return;

    const handleMessage = (event: MessageEvent) => {
      // ✅ Verify origin in production
      if (event.origin !== 'https://embed.v2.doshi.app') {
        console.warn('Rejected message from:', event.origin);
        return;
      }
      
      try {
        const data: WebviewMessage =
          typeof event.data === "string" ? JSON.parse(event.data) : event.data;

        // When we receive PING from webview, send the auth data
        if (data.type === "PING") {
          handleSendAuth();
        }
      } catch (error) {
        console.error("Error processing message:", error);
      }
    };

    window.addEventListener("message", handleMessage);
    return () => window.removeEventListener("message", handleMessage);
  }, [authToken]);

  const handleSendAuth = () => {
    if (!authToken) return;

    // Build auth data object
    const authData: AuthData = {
      token: authToken,
      type: "AUTH"
    };

    // Add optional fields
    if (userEmail) authData.email = userEmail;
    if (segment) authData.segment = segment;
    if (branchId) authData.branchId = branchId;

    // Add 2FA fields if enabled
    if (is2FaEnabled) {
      authData.is2FaEnabled = true;
      if (dob) authData.dob = dob;
      if (organizationId) authData.organizationId = organizationId;
      if (partnerUserId) authData.partnerUserId = partnerUserId;
      if (firstName) authData.firstName = firstName;
      if (lastName) authData.lastName = lastName;
    }

    // Send to iframe
    const webview = document.querySelector("iframe");
    if (webview && webview.contentWindow) {
      webview.contentWindow.postMessage(
        JSON.stringify(authData),
        "https://embed.v2.doshi.app" // ⚠️ Never use "*" in production
      );
    }
  };

  if (isLoading) {
    return (
      <div className="flex items-center justify-center h-screen">
        <div className="text-center">
          <div className="spinner mb-4"></div>
          <p>Loading...</p>
        </div>
      </div>
    );
  }

  if (error) {
    return (
      <div className="flex items-center justify-center h-screen">
        <div className="text-center text-red-600">
          <p>{error}</p>
          <button 
            onClick={() => window.location.reload()}
            className="mt-4 px-4 py-2 bg-blue-600 text-white rounded"
          >
            Retry
          </button>
        </div>
      </div>
    );
  }

  if (!authToken) {
    return <div>Failed to authenticate</div>;
  }

  return (
    <div className="webview-container h-screen w-full">
      <iframe
        src="https://embed.v2.doshi.app"
        className="h-full w-full"
        frameBorder="0"
        allowFullScreen
      />
    </div>
  );
};

export default WebviewComponent;

Usage Example

import WebviewComponent from './WebviewComponent';

function App() {
  return (
    <div className="app">
      <h1>My Application</h1>
      <WebviewComponent 
        userEmail="user@example.com"
        segment="premium"
        branchId="branch_789"
      />
    </div>
  );
}

// With 2FA enabled
function AppWith2FA() {
  return (
    <div className="app">
      <h1>My Application</h1>
      <WebviewComponent 
        userEmail="user@example.com"
        segment="premium"
        branchId="branch_789"
        is2FaEnabled={true}
        dob="1990-01-15"
        organizationId="org_123"
        partnerUserId="partner_123"
        firstName="John"
        lastName="Doe"
      />
    </div>
  );
}

Vanilla JavaScript Implementation

Parent Window

// Configuration
const config = {
  doshiEmbedUrl: 'https://embed.v2.doshi.app',
  backendUrl: '/api/generate-doshi-token'
};

// User data
const userData = {
  email: "user@example.com",
  segment: "premium",
  branchId: "branch_789"
};

// 2FA data (optional)
const twoFactorData = {
  is2FaEnabled: true,
  dob: "1990-01-15",
  organizationId: "org_123",
  partnerUserId: "partner_123",
  firstName: "John",
  lastName: "Doe"
};

let authToken = null;

// Step 1: Get nonce token from your backend
async function fetchAuthToken() {
  try {
    const response = await fetch(config.backendUrl, {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json'
      },
      body: JSON.stringify({
        email: userData.email,
        branchId: userData.branchId
      })
    });

    if (!response.ok) {
      throw new Error('Failed to generate token');
    }

    const data = await response.json();
    authToken = data.token;
    
    // Create iframe after token is ready
    createWebview();
  } catch (error) {
    console.error('Failed to fetch auth token:', error);
    showError('Authentication failed. Please try again.');
  }
}

// Step 2: Create and add webview to the page
function createWebview() {
  const webview = document.createElement("iframe");
  webview.src = config.doshiEmbedUrl;
  webview.className = "h-full w-full";
  webview.frameBorder = "0";
  webview.allowFullscreen = true;

  document.querySelector("#doshi-container").appendChild(webview);
  
  // Setup message listener
  setupMessageListener();
}

// Step 3: Handle messages from webview
function setupMessageListener() {
  window.addEventListener("message", handleMessage);
  
  // Cleanup on page unload
  window.addEventListener("beforeunload", () => {
    window.removeEventListener("message", handleMessage);
  });
}

function handleMessage(event) {
  // ✅ Verify origin in production
  if (event.origin !== config.doshiEmbedUrl) {
    console.warn('Rejected message from:', event.origin);
    return;
  }
  
  try {
    const data = typeof event.data === "string" 
      ? JSON.parse(event.data) 
      : event.data;

    // When we receive PING from webview, send the auth data
    if (data.type === "PING") {
      sendAuthData();
    } else if (data.type === "AUTH_SUCCESS") {
      console.log('Authentication successful');
      onAuthSuccess(data);
    } else if (data.type === "AUTH_ERROR") {
      console.error('Authentication failed:', data.error);
      onAuthError(data.error);
    }
  } catch (error) {
    console.error("Error processing message:", error);
  }
}

// Step 4: Send auth data to webview
function sendAuthData() {
  if (!authToken) {
    console.error('No auth token available');
    return;
  }

  // Build auth data
  const authData = {
    token: authToken,
    email: userData.email,
    segment: userData.segment,
    branchId: userData.branchId,
    type: "AUTH"
  };

  // Add 2FA data if enabled
  if (twoFactorData.is2FaEnabled) {
    Object.assign(authData, twoFactorData);
  }

  // Send to webview
  const webview = document.querySelector("iframe");
  if (webview && webview.contentWindow) {
    webview.contentWindow.postMessage(
      JSON.stringify(authData),
      config.doshiEmbedUrl // ⚠️ Never use "*" in production
    );
  }
}

// Callback functions
function onAuthSuccess(data) {
  console.log('User authenticated:', data);
  // Hide loading indicator, update UI, etc.
}

function onAuthError(error) {
  console.error('Authentication error:', error);
  showError('Authentication failed. Please try again.');
}

function showError(message) {
  const container = document.querySelector("#doshi-container");
  container.innerHTML = `
    <div class="error-message">
      <p>${message}</p>
      <button onclick="window.location.reload()">Retry</button>
    </div>
  `;
}

// Initialize
fetchAuthToken();

HTML Structure

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Doshi Integration</title>
  <style>
    #doshi-container {
      width: 100%;
      height: 100vh;
      position: relative;
    }
    
    .error-message {
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      height: 100vh;
      text-align: center;
    }
    
    .error-message button {
      margin-top: 1rem;
      padding: 0.5rem 1rem;
      background-color: #3b82f6;
      color: white;
      border: none;
      border-radius: 0.375rem;
      cursor: pointer;
    }
  </style>
</head>
<body>
  <div id="doshi-container"></div>
  <script src="doshi-integration.js"></script>
</body>
</html>

Backend Implementation

Your backend should handle the API key securely:

// backend/routes/auth.ts
import express from 'express';

const router = express.Router();

router.post('/generate-doshi-token', async (req, res) => {
  try {
    // Verify user is authenticated in your system
    if (!req.session?.userId) {
      return res.status(401).json({ error: 'Unauthorized' });
    }

    const { email, branchId } = req.body;

    // Call Doshi API with your API key
    const response = await fetch(
      'https://api.doshi.app/client/auth/token',
      {
        method: 'POST',
        headers: {
          'Authorization': `Bearer ${process.env.DOSHI_API_KEY}`,
          'Access-Type': 'client'
          'Content-Type': 'application/json'
        },
        body: JSON.stringify({
          email,
          partnerUserId: req.session.userId,
          branchId
        })
      }
    );

    if (!response.ok) {
      throw new Error('Doshi API request failed');
    }

    const data = await response.json();
    
    // Log for security monitoring
    console.log(`Generated token for user ${req.session.userId}`);
    
    res.json({ token: data.token });
  } catch (error) {
    console.error('Error generating Doshi token:', error);
    res.status(500).json({ error: 'Failed to generate authentication token' });
  }
});

export default router;

Child Window (Webview) Implementation

This section is for reference only. The Doshi iframe already implements this functionality.

Sending PING

// Inside the webview, send PING to parent when ready
window.parent.postMessage(
  JSON.stringify({ type: "PING" }),
  "*" // ⚠️ In production: specify parent origin if known
);

Receiving AUTH Data

// Listen for AUTH response from parent
window.addEventListener("message", (event) => {
  // ✅ Verify origin in production
  // if (event.origin !== 'https://parent-domain.com') return;
  
  try {
    const data = typeof event.data === "string" 
      ? JSON.parse(event.data) 
      : event.data;
    
    if (data.type === "AUTH") {
      // Process authentication data
      const { 
        token, 
        email, 
        segment, 
        branchId,
        is2FaEnabled,
        dob,
        organizationId,
        partnerUserId,
        firstName,
        lastName
      } = data;
      
      // Authenticate user with token
      await authenticateUser(token);
      
      // If 2FA is enabled, show OTP screen
      if (is2FaEnabled) {
        await handle2FAFlow({
          dob,
          organizationId,
          partnerUserId,
          firstName,
          lastName
        });
      }
      
      // Notify parent of success
      window.parent.postMessage(
        JSON.stringify({ 
          type: "AUTH_SUCCESS",
          userId: user.id 
        }),
        event.origin
      );
    }
  } catch (error) {
    console.error("Error processing auth message:", error);
    
    // Notify parent of error
    window.parent.postMessage(
      JSON.stringify({ 
        type: "AUTH_ERROR",
        error: error.message 
      }),
      event.origin
    );
  }
});

Advanced: Retry Logic

Add retry logic for more robust authentication:

const WebviewWithRetry: React.FC<Props> = ({ userEmail }) => {
  const [retryCount, setRetryCount] = useState(0);
  const MAX_RETRIES = 3;
  const RETRY_DELAY = 2000; // 2 seconds

  const handleSendAuth = async () => {
    try {
      const authData = {
        token: authToken,
        email: userEmail,
        type: "AUTH"
      };

      const webview = document.querySelector("iframe");
      if (webview && webview.contentWindow) {
        webview.contentWindow.postMessage(
          JSON.stringify(authData),
          "https://embed.v2.doshi.app"
        );
      } else {
        throw new Error("Webview not found");
      }
    } catch (error) {
      console.error("Error sending auth:", error);
      
      if (retryCount < MAX_RETRIES) {
        console.log(`Retrying... (${retryCount + 1}/${MAX_RETRIES})`);
        setTimeout(() => {
          setRetryCount(retryCount + 1);
          handleSendAuth();
        }, RETRY_DELAY);
      } else {
        setError('Failed to authenticate after multiple attempts');
      }
    }
  };

  // ... rest of component
};

Message Types

type

string

required

The message type identifier

Show Available Types

From Iframe to Parent:

PING: Sent by webview to signal readiness
AUTH_SUCCESS: Authentication completed successfully
AUTH_ERROR: Authentication failed

From Parent to Iframe:

AUTH: Sent by parent with authentication data

Testing postMessage Flow

// Test the authentication flow
function testPostMessageFlow() {
  console.log('Testing postMessage flow...');
  
  // Simulate PING from iframe
  window.postMessage(
    JSON.stringify({ type: "PING" }),
    window.location.origin
  );
  
  // Listen for AUTH response
  window.addEventListener("message", (event) => {
    const data = JSON.parse(event.data);
    console.log("Received message:", data);
    
    if (data.type === "AUTH") {
      console.log("✅ AUTH message received");
      console.log("Token:", data.token);
      console.log("Email:", data.email);
    }
  });
}

Common Issues

Messages not being received

Solutions:

Check that origin validation matches exactly
Verify iframe has loaded before sending messages
Ensure JSON.stringify is used when sending data
Check browser console for errors

Token not available

Solutions:

Ensure backend API call completed successfully
Check network tab for API response
Verify error handling in token fetch logic
Check that API key is valid

2FA not triggering

Solutions:

Verify is2FaEnabled is set to true
Ensure all required 2FA fields are provided
Check that organization has 2FA enabled
Verify user phone number is registered

Next Steps

Security Guidelines

Review security best practices

Best Practices

Optimize your implementation

​Overview

​How It Works

​TypeScript Interfaces

​React Implementation

​Complete Example with API Call

​Usage Example

​Vanilla JavaScript Implementation

​Parent Window

​HTML Structure

​Backend Implementation

​Child Window (Webview) Implementation

​Sending PING

​Receiving AUTH Data

​Advanced: Retry Logic

​Message Types

​Testing postMessage Flow

​Common Issues

​Next Steps

Security Guidelines

Best Practices

Overview

How It Works

TypeScript Interfaces

React Implementation

Complete Example with API Call

Usage Example

Vanilla JavaScript Implementation

Parent Window

HTML Structure

Backend Implementation

Child Window (Webview) Implementation

Sending PING

Receiving AUTH Data

Advanced: Retry Logic

Message Types

Testing postMessage Flow

Common Issues

Next Steps