JsonRpcProvider: Basic access authentication support

With this patch, `JsonRpcProvider` accepts a url with basic authentication
credentials like this:

```
const PoktEndpoint = 'https://scott:[email protected]';
const provider = new JsonRpcProvider({
  rpcUrl: PoktEndpoint,
  dispatchers: [PoktEndpoint],
});
```

README.md

@@ -27,6 +27,10 @@ import {
 } from "./config.js";
 
 // Instantiate a provider for querying information on the chain!
+//
+// MAINNET_RPC_URL and an element of DISPATCHERS is a string representing an
+// endpoint URL to the Pocket Network which may or may not contains basic
+// authentication credentials e.g. "https://scott:[email protected]".
 export const provider = new JsonRpcProvider({
   rpcUrl: MAINNET_RPC_URL,
   // If you'll Instantiate a relayer, you need to add dispatchers as well

packages/provider/src/json-rpc-provider.ts

@@ -93,14 +93,25 @@ export class JsonRpcProvider implements AbstractProvider {
         ]
       : this.rpcUrl
 
-    const routedRpcUrl = `${finalRpcUrl}${route}`
+    const headers = {
+      'Content-Type': 'application/json',
+    };
+
+    const url = new URL(route, finalRpcUrl);
+    if (url.username || url.password) {
+      const credential =
+        Buffer.from(`${url.username}:${url.password}`).toString('base64');
+      headers['Authorization'] = `Basic ${credential}`;
+      url.username = '';
+      url.password = '';
+    }
+
+    const routedRpcUrl = url.toString();
 
     const rpcResponse = await fetch(routedRpcUrl, {
       method: 'POST',
       signal: controller.signal as AbortSignal,
-      headers: {
-        'Content-Type': 'application/json',
-      },
+      headers: headers,
       body: JSON.stringify(body),
     }).catch((error) => {
       debug(`${routedRpcUrl} attempt ${retriesPerformed + 1} failure`)