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Cross-domain authentication

When your Agents are deployed, to keep things secure, send a token from the client, then verify it on the server. This guide covers authentication patterns for WebSocket connections to agents.

WebSocket authentication

WebSockets are not HTTP, so the handshake is limited when making cross-domain connections.

You cannot send:

You can:

Same origin

If the client and server share the origin, the browser will send cookies during the WebSocket handshake. Session-based auth can work here. Prefer HTTP-only cookies.

Cross origin

Cross-origin cookie behavior depends on the cookie's domain and SameSite attributes, whether the two origins are same-site, and browser third-party cookie policy. If you cannot rely on a cookie, pass a short-lived credential in the URL query and verify it on the server.

Usage examples

Static authentication

import { useAgent } from "agents/react";

function ChatComponent() {
	const agent = useAgent({
		agent: "my-agent",
		query: {
			token: "demo-token-123",
			userId: "demo-user",
		},
	});

	// Use agent to make calls, access state, etc.
}
import { useAgent } from "agents/react";

function ChatComponent() {
	const agent = useAgent({
		agent: "my-agent",
		query: {
			token: "demo-token-123",
			userId: "demo-user",
		},
	});

	// Use agent to make calls, access state, etc.
}

Async authentication

Build query values right before connect. Use Suspense for async setup.

import { useAgent } from "agents/react";
import { Suspense, useCallback } from "react";

function ChatComponent() {
	const asyncQuery = useCallback(async () => {
		const [token, user] = await Promise.all([getAuthToken(), getCurrentUser()]);
		return {
			token,
			userId: user.id,
			timestamp: Date.now().toString(),
		};
	}, []);

	const agent = useAgent({
		agent: "my-agent",
		query: asyncQuery,
	});

	// Use agent to make calls, access state, etc.
}

function App() {
	return (
		<Suspense fallback={<div>Authenticating...</div>}>
			<ChatComponent />
		</Suspense>
	);
}
import { useAgent } from "agents/react";
import { Suspense, useCallback } from "react";

function ChatComponent() {
	const asyncQuery = useCallback(async () => {
		const [token, user] = await Promise.all([getAuthToken(), getCurrentUser()]);
		return {
			token,
			userId: user.id,
			timestamp: Date.now().toString(),
		};
	}, []);

	const agent = useAgent({
		agent: "my-agent",
		query: asyncQuery,
	});

	// Use agent to make calls, access state, etc.
}

function App() {
	return (
		<Suspense fallback={<div>Authenticating...</div>}>
			<ChatComponent />
		</Suspense>
	);
}

JWT refresh pattern

useAgent resolves an async query before connecting and reevaluates it when reconnecting. Return a fresh, short-lived application token each time:

import { useAgent } from "agents/react";
import { useCallback } from "react";

function useJWTAgent(agentName) {
	const asyncQuery = useCallback(async () => {
		return { token: await getShortLivedAccessToken() };
	}, []);

	return useAgent({
		agent: agentName,
		query: asyncQuery,
	});
}
import { useAgent } from "agents/react";
import { useCallback } from "react";

declare function getShortLivedAccessToken(): Promise<string>;

function useJWTAgent(agentName: string) {
	const asyncQuery = useCallback(async () => {
		return { token: await getShortLivedAccessToken() };
	}, []);

	return useAgent({
		agent: agentName,
		query: asyncQuery,
	});
}

Cross-domain authentication

Pass credentials in the URL when connecting to another host, then verify on the server.

Static cross-domain auth

import { useAgent } from "agents/react";

function StaticCrossDomainAuth() {
	const agent = useAgent({
		agent: "my-agent",
		host: "https://my-agent.example.workers.dev",
		query: {
			token: "demo-token-123",
			userId: "demo-user",
		},
	});

	// Use agent to make calls, access state, etc.
}
import { useAgent } from "agents/react";

function StaticCrossDomainAuth() {
	const agent = useAgent({
		agent: "my-agent",
		host: "https://my-agent.example.workers.dev",
		query: {
			token: "demo-token-123",
			userId: "demo-user",
		},
	});

	// Use agent to make calls, access state, etc.
}

Async cross-domain auth

import { useAgent } from "agents/react";
import { useCallback } from "react";

function AsyncCrossDomainAuth() {
	const asyncQuery = useCallback(async () => {
		const [token, user] = await Promise.all([getAuthToken(), getCurrentUser()]);
		return {
			token,
			userId: user.id,
			timestamp: Date.now().toString(),
		};
	}, []);

	const agent = useAgent({
		agent: "my-agent",
		host: "https://my-agent.example.workers.dev",
		query: asyncQuery,
	});

	// Use agent to make calls, access state, etc.
}
import { useAgent } from "agents/react";
import { useCallback } from "react";

function AsyncCrossDomainAuth() {
	const asyncQuery = useCallback(async () => {
		const [token, user] = await Promise.all([getAuthToken(), getCurrentUser()]);
		return {
			token,
			userId: user.id,
			timestamp: Date.now().toString(),
		};
	}, []);

	const agent = useAgent({
		agent: "my-agent",
		host: "https://my-agent.example.workers.dev",
		query: asyncQuery,
	});

	// Use agent to make calls, access state, etc.
}

Server-side verification

On the server side, verify the token in the onConnect handler:

import { Agent, Connection, ConnectionContext } from "agents";

export class SecureAgent extends Agent {
	async onConnect(connection, ctx) {
		const url = new URL(ctx.request.url);
		const token = url.searchParams.get("token");
		const userId = url.searchParams.get("userId");

		// Verify the token
		if (!token || !(await this.verifyToken(token, userId))) {
			connection.close(4001, "Unauthorized");
			return;
		}

		// Store user info on the connection state
		connection.setState({ userId, authenticated: true });
	}

	async verifyToken(token, userId) {
		// Implement your token verification logic
		// For example, verify a JWT signature, check expiration, etc.
		try {
			const payload = await verifyJWT(token, this.env.JWT_SECRET);
			return payload.sub === userId && payload.exp > Date.now() / 1000;
		} catch {
			return false;
		}
	}

	async onMessage(connection, message) {
		// Check if connection is authenticated
		if (!connection.state?.authenticated) {
			connection.send(JSON.stringify({ error: "Not authenticated" }));
			return;
		}

		// Process message for authenticated user
		const userId = connection.state.userId;
		// ...
	}
}
import { Agent, Connection, ConnectionContext } from "agents";

export class SecureAgent extends Agent {
	async onConnect(connection: Connection, ctx: ConnectionContext) {
		const url = new URL(ctx.request.url);
		const token = url.searchParams.get("token");
		const userId = url.searchParams.get("userId");

		// Verify the token
		if (!token || !(await this.verifyToken(token, userId))) {
			connection.close(4001, "Unauthorized");
			return;
		}

		// Store user info on the connection state
		connection.setState({ userId, authenticated: true });
	}

	private async verifyToken(token: string, userId: string): Promise<boolean> {
		// Implement your token verification logic
		// For example, verify a JWT signature, check expiration, etc.
		try {
			const payload = await verifyJWT(token, this.env.JWT_SECRET);
			return payload.sub === userId && payload.exp > Date.now() / 1000;
		} catch {
			return false;
		}
	}

	async onMessage(connection: Connection, message: string) {
		// Check if connection is authenticated
		if (!connection.state?.authenticated) {
			connection.send(JSON.stringify({ error: "Not authenticated" }));
			return;
		}

		// Process message for authenticated user
		const userId = connection.state.userId;
		// ...
	}
}

Best practices

  1. Use short-lived tokens - Tokens in URLs may be logged. Keep expiration times short (minutes, not hours).

  2. Scope tokens appropriately - Include the agent name or instance in the token claims to prevent token reuse across agents.

  3. Validate on every connection - Always verify tokens in onConnect, not just once.

  4. Use HTTPS - Always use secure WebSocket connections (wss://) in production.

  5. Rotate secrets - Regularly rotate your JWT signing keys or token secrets.

  6. Log authentication failures - Track failed authentication attempts for security monitoring.

Next steps

Routing

Routing and authentication hooks.

WebSockets

Real-time bidirectional communication.

GitHub OAuth agent example

Protect an app built with Agents using GitHub OAuth, HTTP-only cookies, and server-owned Durable Object routing.

Agents API

Complete API reference for the Agents SDK.