anthropic[patch]: Pass custom headers through to request (#6275)

* anthropic[patch]: Pass custom headers through to request

* chore: lint files

libs/langchain-anthropic/src/chat_models.ts

@@ -61,6 +61,11 @@ export interface ChatAnthropicCallOptions
    * @default "auto"
    */
   tool_choice?: AnthropicToolChoice;
+  /**
+   * Custom headers to pass to the Anthropic API
+   * when making a request.
+   */
+  headers?: Record<string, string>;
 }
 
 function _toolsInParams(params: AnthropicMessageCreateParams): boolean {
@@ -422,11 +427,16 @@ export class ChatAnthropicMessages<
       stream: false,
     });
 
-    const stream = await this.createStreamWithRetry({
-      ...params,
-      ...formattedMessages,
-      stream: true,
-    });
+    const stream = await this.createStreamWithRetry(
+      {
+        ...params,
+        ...formattedMessages,
+        stream: true,
+      },
+      {
+        headers: options.headers,
+      }
+    );
 
     for await (const data of stream) {
       if (options.signal?.aborted) {
@@ -543,6 +553,7 @@ export class ChatAnthropicMessages<
     } else {
       return this._generateNonStreaming(messages, params, {
         signal: options.signal,
+        headers: options.headers,
       });
     }
   }