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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:

  • Custom headers during the upgrade
  • Authorization: Bearer ... on connect

You can:

  • Put a signed, short-lived token in the connection URL as query parameters
  • Verify the token in your server's connect path

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

Cookies do not help across origins. Pass credentials in the URL query, then verify on the server.

Usage examples

Static authentication

JavaScript
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.

JavaScript
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

Refresh the token when the connection fails due to authentication error.

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


const validateToken = async (token) => {
  // An example of how you might implement this
  const res = await fetch(`${API_HOST}/api/users/me`, {
    headers: {
      Authorization: `Bearer ${token}`,
    },
  });


  return res.ok;
};


const refreshToken = async () => {
  // Depends on implementation:
  // - You could use a longer-lived token to refresh the expired token
  // - De-auth the app and prompt the user to log in manually
  // - ...
};


function useJWTAgent(agentName) {
  const asyncQuery = useCallback(async () => {
    let token = localStorage.getItem("jwt");


    // If no token OR the token is no longer valid
    // request a fresh token
    if (!token || !(await validateToken(token))) {
      token = await refreshToken();
      localStorage.setItem("jwt", token);
    }


    return {
      token,
    };
  }, []);


  const agent = useAgent({
    agent: agentName,
    query: asyncQuery,
    queryDeps: [], // Run on mount
  });


  return agent;
}

Cross-domain authentication

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

Static cross-domain auth

JavaScript
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

JavaScript
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:

JavaScript
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;
    // ...
  }
}

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.
Agents API Complete API reference for the Agents SDK.