google-genai: support of adding custom headers on ChatGoogleGenerativeAI #6648 (#8327)

Co-authored-by: Hunter Lovell <40191806+hntrl@users.noreply.github.com>
Co-authored-by: Hunter Lovell <hunter@hntrl.io>

Author: caspherola

.changeset/bright-numbers-vanish.md

@@ -0,0 +1,5 @@
+---
+"@langchain/google-genai": patch
+---
+
+support of adding custom headers on ChatGoogleGenerativeAI #6648

libs/providers/langchain-google-genai/src/chat_models.ts

@@ -185,6 +185,11 @@ export interface GoogleGenerativeAIChatInput
    */
   baseUrl?: string;
 
+  /**
+   * Google API custom headers to use
+   */
+  customHeaders?: Record<string, string>;
+
   /** Whether to stream the results or not */
   streaming?: boolean;
 
@@ -727,6 +732,7 @@ export class ChatGoogleGenerativeAI
       {
         apiVersion: fields.apiVersion,
         baseUrl: fields.baseUrl,
+        customHeaders: fields.customHeaders,
       }
     );
     this.streamUsage = fields.streamUsage ?? this.streamUsage;