rtm-api: add support for custom webClient (#1696)

docs/_packages/rtm_api.md

@@ -644,6 +644,30 @@ const rtm = new RTMClient(token, options);
 
 ---
 
+### Custom WebClient
+
+In some cases, you might want to customize the underlying component making HTTP requests to the Slack API, the [`WebClient`](reference/web-api#webclient), beyond the provided [`RTMClientOptions`](reference/rtm-api#rtmclientoptions). Note that overriding the [`WebClient`](reference/web-api#webclient) instance takes precedence over any other [`RTMClientOptions`](reference/rtm-api#rtmclientoptions) specified.
+
+```javascript
+const { RTMClient } = require('@slack/rtm-api');
+const { WebClient, WebClientOptions } = require('@slack/web-api');
+const token = process.env.SLACK_BOT_TOKEN;
+
+// Configure the client to have custom headers
+const options = {
+  headers: {
+     'Cookie': 'myCookie=cookieValue;'
+  }
+} as WebClientOptions;
+
+const webClient = new WebClient(token, options);
+
+// Initialize a client using the configuration
+const rtm = new RTMClient(token, { webClient });
+```
+
+---
+
 ### Workspace state snapshot
 
 The client can receive a snapshot of a portion of the workspace's state while its connecting. This can be useful if your

docs/_reference/rtm-api.md

@@ -15,6 +15,7 @@ slug: rtm-api
 <th align="center">Name</th>
 <th align="center">Type</th>
 <th align="center">Required</th>
+<th align="center">Description</th>
 <th></th>
 </tr>
 </thead>
@@ -31,6 +32,13 @@ slug: rtm-api
 <td align="center">✗</td>
 <td></td>
 </tr>
+<tr>
+<td align="center">webClient</td>
+<td align="center"><code><a href="web-api#webclient" title="">WebClient</a></code></td>
+<td align="center">✗</td>
+<td align="center">An optional parameter to provide a customized <a href="web-api#webclient">WebClient</a>. Any desired options for the custom client must be set in this parameter (<code>webClient</code>) as they will take precedence over other arguments passed into <code>RTMClient</code>.</td>
+<td></td>
+</tr>
 </tbody>
 </table>
 <strong>Options:</strong>

packages/rtm-api/src/RTMClient.ts

@@ -348,9 +348,10 @@ export class RTMClient extends EventEmitter {
     serverPongTimeout,
     replyAckOnReconnectTimeout = 2000,
     tls = undefined,
+    webClient,
   }: RTMClientOptions = {}) {
     super();
-    this.webClient = new WebClient(token, {
+    this.webClient = webClient || new WebClient(token, {
       slackApiUrl,
       logger,
       logLevel,
@@ -672,6 +673,7 @@ export default RTMClient;
  */
 
 export interface RTMClientOptions {
+  webClient?: WebClient;
   slackApiUrl?: string;
   logger?: Logger;
   logLevel?: LogLevel;