docs: Example for customizing fetch requests to trustless gateways

packages/block-brokers/README.md

@@ -27,6 +27,46 @@ Loading this module through a script tag will make its exports available as `Hel
 <script src="https://unpkg.com/@helia/block-brokers/dist/index.min.js"></script>
 ```
 
+# Example - Customizing trustless gateway requests
+
+```typescript
+import { TrustlessGatewayBlockBroker } from "@helia/block-brokers/trustless-gateway/broker.js";
+import { defaultLogger } from "@libp2p/logger";
+import { CID } from "multiformats/cid";
+
+// Create a trustless gateway block broker with custom request options
+const gatewayBlockBroker = new TrustlessGatewayBlockBroker(
+  {
+    routing, // Your routing implementation
+    logger: defaultLogger(),
+  },
+  {
+    allowInsecure: true,
+    allowLocal: true,
+    // Add a transformRequestInit function to customize the fetch request
+    transformRequestInit: (requestInit) => {
+      // Add authentication headers for your gateway
+      requestInit.headers = {
+        ...requestInit.headers,
+        Authorization: "Bearer your-jwt-token-here",
+      };
+      return requestInit;
+    },
+  }
+);
+
+// Use the block broker to retrieve blocks
+const cid = CID.parse(
+  "bafybeic3q4y65yxu3yckr76q63bcvanhklwf6cwxuacnrot6v3gykrgsvq"
+);
+const block = await gatewayBlockBroker.retrieve?.(cid, {
+  validateFn: async (block) => {
+    // Optional validation function
+    // You can validate the retrieved block here
+  },
+});
+```
+
 # API Docs
 
 - <https://ipfs.github.io/helia/modules/_helia_block_brokers.html>