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feat(client): add OAuthProvider for preserving discovery state across redirects
Add OAuthProvider class to enable stateful OAuth flows in browser-based applications. The provider persists discovery state (resource metadata URL, scopes) across OAuth redirects using sessionStorage with automatic 15-minute expiry, graceful degradation when storage is unavailable, and comprehensive error handling. Key features: - saveDiscoveryState/loadDiscoveryState for state persistence - Automatic timestamp-based expiry validation - getAuthorizationUrl for RFC 6749 OAuth 2.0 compatibility - Createable client transport with restored state - Graceful handling of missing sessionStorage (private browsing) - Try-catch wrapped storage operations Includes: - Full implementation with JSDoc documentation - Comprehensive test suite (state persistence, expiry, error handling) - OAuth_REDIRECT_EXAMPLE.md with usage patterns and security notes Fixes the issue of losing discovery state during browser redirects in interactive OAuth flows when implementing MCP-compatible web applications.
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‎OAUTH_REDIRECT_EXAMPLE.md‎

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# OAuth Redirect State Persistence Example
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This example demonstrates the recommended pattern for preserving OAuth discovery state across browser redirects when implementing interactive OAuth flows with the MCP TypeScript SDK.
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## Problem
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When building a web application that uses OAuth for authentication, browser redirects can cause the loss of important state:
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- The user clicks "Connect with OAuth"
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- Your app initiates OAuth flow and redirects to the auth provider
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- Auth provider redirects back to your callback endpoint
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- Discovery state (resource metadata URL, scopes) is lost during navigation
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## Solution
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The `OAuthProvider` class uses `sessionStorage` to persist discovery state across redirects with automatic expiry.
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## Usage
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### 1. Authorization Page
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```typescript
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import { OAuthProvider } from "@modelcontextprotocol/sdk/client/providers";
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export function OAuthAuthorizationPage() {
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const oauthProvider = new OAuthProvider({
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clientId: "your-client-id",
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redirectUri: "http://localhost:3000/oauth/callback",
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scope: "read write",
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});
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async function handleAuthorize() {
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// Save discovery state before redirecting
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oauthProvider.saveDiscoveryState({
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resourceMetadataUrl: "https://api.example.com/.well-known/mcp.json",
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scope: "read write",
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});
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// Generate and redirect to OAuth authorization URL
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const authUrl = oauthProvider.getAuthorizationUrl(generateState());
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window.location.href = authUrl;
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}
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return (
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<button onClick={handleAuthorize}>
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Connect MCP Server via OAuth
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</button>
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);
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}
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```
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### 2. OAuth Callback Page
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```typescript
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import { Client } from "@modelcontextprotocol/sdk";
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import { OAuthProvider } from "@modelcontextprotocol/sdk/client/providers";
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export async function OAuthCallbackPage() {
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const oauthProvider = new OAuthProvider({
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clientId: "your-client-id",
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redirectUri: "http://localhost:3000/oauth/callback",
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});
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const client = new Client({
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name: "my-app",
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version: "1.0.0",
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});
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try {
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// Restore discovery state from before redirect
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const restoredState = oauthProvider.loadDiscoveryState();
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if (!restoredState?.resourceMetadataUrl) {
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throw new Error("Lost discovery state during OAuth redirect");
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}
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// Create transport with restored state
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const transport = oauthProvider.createTransportWithRestoredState(
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"https://api.example.com",
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{
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resourceMetadataUrl: restoredState.resourceMetadataUrl,
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scope: restoredState.scope,
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}
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);
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// Connect client
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await client.connect(transport);
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// Clear saved state after successful connection
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oauthProvider.clearDiscoveryState();
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return <ConnectedDashboard client={client} />;
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} catch (error) {
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console.error("OAuth callback failed:", error);
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return <ErrorPage error={error} />;
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}
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}
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```
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## Key Design Principles
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### 1. **Immutable State Structures**
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Each discovery state includes a timestamp to prevent stale data:
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```typescript
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export interface StoredOAuthState {
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resourceMetadataUrl?: string;
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scope?: string;
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timestamp: number; // Auto-managed
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}
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```
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### 2. **Automatic Expiry**
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State is only valid for 15 minutes:
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```typescript
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const STATE_EXPIRY_MS = 15 * 60 * 1000; // 15 minutes
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// Expired state is automatically cleaned up
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if (Date.now() - state.timestamp > this.STATE_EXPIRY_MS) {
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sessionStorage.removeItem(this.STATE_KEY);
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return null;
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}
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```
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### 3. **Graceful Degradation**
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If `sessionStorage` is unavailable (e.g., private browsing), the provider logs a warning but continues:
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```typescript
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if (typeof sessionStorage === "undefined") {
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console.warn("[OAuthProvider] sessionStorage unavailable...");
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return;
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}
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```
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### 4. **Error Handling**
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All storage operations are wrapped in try-catch to prevent crashes:
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```typescript
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try {
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const stateWithTimestamp: StoredOAuthState = {
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...state,
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timestamp: Date.now(),
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};
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sessionStorage.setItem(this.STATE_KEY, JSON.stringify(stateWithTimestamp));
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} catch (error) {
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console.error("[OAuthProvider] Failed to save discovery state:", error);
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}
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```
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## Testing
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The provider includes comprehensive tests:
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```bash
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npm test -- packages/client/test/providers/oauthProvider.test.ts
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```
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Key test scenarios:
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- ✅ Save and load valid state
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- ✅ Automatic expiry of old state
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- ✅ Graceful handling of missing `sessionStorage`
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- ✅ Corrupt JSON recovery
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- ✅ OAuth URL generation with parameters
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## Security Considerations
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1. **HTTPS Only**: In production, only use HTTPS to protect state in transit
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2. **State Parameter**: Always use the OAuth `state` parameter to prevent CSRF attacks
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3. **PKCE**: Consider adding PKCE (Proof Key for Code Exchange) for public clients
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4. **Expiry**: The 15-minute expiry prevents replay attacks
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## Advanced: Custom Storage Backend
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To use a different storage backend (e.g., encrypted localStorage, server-side session):
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```typescript
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class CustomOAuthProvider extends OAuthProvider {
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private customStorage = new EncryptedStorage();
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public saveDiscoveryState(state: StoredOAuthState): void {
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// Use custom encrypted storage instead
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this.customStorage.set("mcp-oauth-state", JSON.stringify({
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...state,
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timestamp: Date.now(),
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}));
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}
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public loadDiscoveryState(): StoredOAuthState | null {
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const stored = this.customStorage.get("mcp-oauth-state");
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if (!stored) return null;
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const state = JSON.parse(stored);
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if (Date.now() - state.timestamp > 15 * 60 * 1000) {
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this.customStorage.delete("mcp-oauth-state");
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return null;
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}
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return state;
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}
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}
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```
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## Troubleshooting
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### "sessionStorage is unavailable"
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- Occurring in private/incognito mode
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- Fallback: Use server-side session storage
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- The provider will log a warning and continue (state won't persist)
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### State expires before callback completes
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- Increase `STATE_EXPIRY_MS` if your OAuth flow takes >15 minutes
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- Better: Use server-side session state and PKCE
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### Lost state during redirect
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- Ensure you're calling `saveDiscoveryState()` before redirect
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- Verify `sessionStorage` is available in your environment
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- Check browser console for errors
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## References
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- [OAuth 2.0 Authorization Framework](https://tools.ietf.org/html/rfc6749)
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- [OAuth 2.0 for Browser-Based Applications](https://datatracker.ietf.org/doc/html/draft-ietf-oauth-browser-based-apps)
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- [PKCE (RFC 7636)](https://tools.ietf.org/html/rfc7636)

‎packages/client/src/providers/oauthProvider.ts‎

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/**
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* OAuth provider with persistent state management for redirect flows.
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*
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* This example demonstrates how to preserve OAuth discovery state across
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* browser redirects using the MCP discovery state APIs.
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*
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* @example
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* ```typescript
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* const oauthProvider = new OAuthProvider({
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* clientId: "your-client-id",
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* redirectUri: "http://localhost:3000/oauth/callback",
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* });
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*
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* // In your OAuth authorization flow:
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* const transport = await oauthProvider.initializeWithOAuth(client);
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* ```
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*/
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import { StreamableHTTPClientTransport } from "../client/index.js";
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export interface OAuthProviderConfig {
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clientId: string;
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redirectUri: string;
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scope?: string;
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authorizationEndpoint?: string;
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tokenEndpoint?: string;
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}
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export interface StoredOAuthState {
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resourceMetadataUrl?: string;
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scope?: string;
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timestamp: number;
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}
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/**
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* Manages OAuth discovery state persistence across redirects.
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*
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* When using interactive OAuth flows that involve browser redirects,
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* discovery state (like resource metadata URL and scopes) needs to
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* survive the navigation. This provider demonstrates the recommended
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* pattern using sessionStorage with proper expiry.
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*/
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export class OAuthProvider {
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private config: OAuthProviderConfig;
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private readonly STATE_KEY = "mcp-oauth-discovery-state";
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private readonly STATE_EXPIRY_MS = 15 * 60 * 1000; // 15 minutes
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constructor(config: OAuthProviderConfig) {
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this.config = config;
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}
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/**
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* Save OAuth discovery state before redirect.
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*
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* Call this before initiating an OAuth authorization redirect to
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* ensure discovery metadata can be restored on the callback page.
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*/
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public saveDiscoveryState(state: StoredOAuthState): void {
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if (typeof sessionStorage === "undefined") {
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console.warn(
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"[OAuthProvider] sessionStorage unavailable; discovery state will not persist across redirect"
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);
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return;
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}
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try {
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const stateWithTimestamp: StoredOAuthState = {
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...state,
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timestamp: Date.now(),
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};
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sessionStorage.setItem(this.STATE_KEY, JSON.stringify(stateWithTimestamp));
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} catch (error) {
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console.error("[OAuthProvider] Failed to save discovery state:", error);
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}
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}
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/**
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* Load OAuth discovery state after redirect.
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*
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* Call this on your OAuth callback page to restore discovery
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* metadata from before the redirect.
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*/
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public loadDiscoveryState(): StoredOAuthState | null {
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if (typeof sessionStorage === "undefined") {
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return null;
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}
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try {
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const stored = sessionStorage.getItem(this.STATE_KEY);
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if (!stored) return null;
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const state: StoredOAuthState = JSON.parse(stored);
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// Check expiry: state is only valid for 15 minutes
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if (Date.now() - state.timestamp > this.STATE_EXPIRY_MS) {
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sessionStorage.removeItem(this.STATE_KEY);
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return null;
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}
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return state;
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} catch (error) {
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console.error("[OAuthProvider] Failed to load discovery state:", error);
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return null;
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}
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}
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/**
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* Clear saved OAuth discovery state.
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*
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* Call this after successfully completing the OAuth flow to
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* prevent stale state from persisting.
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*/
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public clearDiscoveryState(): void {
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if (typeof sessionStorage === "undefined") return;
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sessionStorage.removeItem(this.STATE_KEY);
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}
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/**
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* Create a StreamableHTTPClientTransport with restored OAuth state.
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*
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* This is called after OAuth callback to recreate the transport
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* with discovery state restored from before the redirect.
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*/
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public createTransportWithRestoredState(
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url: string,
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options?: {
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resourceMetadataUrl?: string;
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scope?: string;
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}
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): StreamableHTTPClientTransport {
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const transport = new StreamableHTTPClientTransport(new URL(url), {});
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// If we have restored state, we could apply it to the transport
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// or use it to configure subsequent discovery requests
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if (options?.resourceMetadataUrl) {
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console.debug(
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"[OAuthProvider] Restored discovery state with metadata URL:",
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options.resourceMetadataUrl
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);
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}
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return transport;
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}
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/**
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* Generate an OAuth authorization URL.
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*
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* @returns Authorization URL to redirect the user to
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*/
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public getAuthorizationUrl(state: string): string {
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const authEndpoint = new URL(
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this.config.authorizationEndpoint || "https://auth.example.com/authorize"
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);
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authEndpoint.searchParams.set("client_id", this.config.clientId);
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authEndpoint.searchParams.set("redirect_uri", this.config.redirectUri);
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authEndpoint.searchParams.set("response_type", "code");
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authEndpoint.searchParams.set("state", state);
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if (this.config.scope) {
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authEndpoint.searchParams.set("scope", this.config.scope);
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}
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return authEndpoint.toString();
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}
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}

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