feat: Add Custom Token Exchange support

[subhankarmaiti]

Adds support for Custom Token Exchange using RFC 8693, enabling users to exchange external identity provider tokens for Auth0 tokens.

What's New

• ✨ customTokenExchange() method on Auth0 class and useAuth0() hook
• 📱 Full native (iOS/Android) and web platform support

Usage

Basic Example

import Auth0 from 'react-native-auth0';

const auth0 = new Auth0({
  domain: 'YOUR_DOMAIN',
  clientId: 'YOUR_CLIENT_ID',
});

try {
  const credentials = await auth0.customTokenExchange({
    subjectToken: 'external-token',
    subjectTokenType: 'urn:acme:legacy-token',
    audience: 'https://api.example.com',
    scope: 'openid profile email',
  });
  
  console.log('Access Token:', credentials.accessToken);
} catch (error) {
  console.error('Token exchange failed:', error.code, error.message);
}

[Copilot]

Pull request overview

This pull request adds Custom Token Exchange support using RFC 8693, enabling users to exchange external identity provider tokens for Auth0 tokens. The implementation provides full native (iOS/Android) and web platform support.

Changes:

• Added customTokenExchange() method to Auth0 class and useAuth0() hook
• Implemented CustomTokenExchangeError class with platform-agnostic error codes for unified error handling
• Added complete native bridge support for iOS (Swift) and Android (Kotlin) implementations

Reviewed changes

Copilot reviewed 23 out of 23 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/types/parameters.ts	Defines CustomTokenExchangeParameters interface with comprehensive documentation
src/specs/NativeA0Auth0.ts	Adds native module spec for customTokenExchange method
src/platforms/web/adapters/WebAuth0Client.ts	Implements web platform token exchange using auth0-spa-js
src/platforms/native/bridge/NativeBridgeManager.ts	Adds native bridge implementation with proper error wrapping
src/platforms/native/adapters/NativeAuth0Client.ts	Integrates customTokenExchange with guarded bridge pattern
src/core/models/CustomTokenExchangeError.ts	Implements comprehensive error class with multi-platform error code mapping
src/hooks/Auth0Provider.tsx	Integrates customTokenExchange into React context and hooks
src/hooks/Auth0Context.ts	Adds interface definition for the new method
src/Auth0.ts	Exposes customTokenExchange on main Auth0 class
src/index.ts	Exports CustomTokenExchangeError and error codes
ios/NativeBridge.swift	Implements iOS native token exchange
ios/A0Auth0.mm	Adds React Native bridge method for iOS
android/src/main/oldarch/com/auth0/react/A0Auth0Spec.kt	Adds Android spec method
android/src/main/java/com/auth0/react/A0Auth0Module.kt	Implements Android native token exchange
EXAMPLES.md	Provides comprehensive usage examples and error handling guide
Test files	Comprehensive test coverage for all implementations

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