feat(firestore-send-email) Attach headers to nodemailer (#108)

Author: Ehesp

firestore-send-email/POSTINSTALL.md

@@ -47,6 +47,7 @@ The top-level fields of the document supply the email sender and recipient infor
 * **ccUids:** An array containing the CC recipient UIDs.
 * **bcc:** A single recipient email address or an array containing multiple recipient email addresses.
 * **bccUids:** An array containing the BCC recipient UIDs.
+* **headers:** An object of additional header fields (for example, `{"X-Custom-Header": "value", "X-Second-Custom-Header": "value"}`).
 
 **NOTE:** The `toUids`, `ccUids`, and `bccUids` options deliver emails based on user UIDs keyed to email addresses within a Cloud Firestore document. To use these recipient options, you need to specify a Cloud Firestore collection for the extension's "Users collection" parameter. The extension can then read the `email` field for each UID specified in the `toUids`, `ccUids`, and/or `bccUids` fields.
 

firestore-send-email/functions/lib/index.js

@@ -198,6 +198,7 @@ function deliver(payload, ref) {
                 to: payload.to,
                 cc: payload.cc,
                 bcc: payload.bcc,
+                headers: payload.headers || {},
             }));
             const info = {
                 messageId: result.messageId || null,

firestore-send-email/functions/src/index.ts

@@ -73,6 +73,7 @@ interface QueuePayload {
   bccUids?: string[];
   from?: string;
   replyTo?: string;
+  headers?: any;
 }
 
 function validateFieldArray(field: string, array?: string[]) {
@@ -262,6 +263,7 @@ async function deliver(
         to: payload.to,
         cc: payload.cc,
         bcc: payload.bcc,
+        headers: payload.headers || {},
       })
     );
     const info = {