Add document unsubscribe link in email footer (#5762)

server/models/helpers/SubscriptionHelper.ts

@@ -0,0 +1,29 @@
+import crypto from "crypto";
+import env from "@server/env";
+
+/**
+ * Helper class for working with subscription settings
+ */
+export default class SubscriptionHelper {
+  /**
+   * Get the unsubscribe URL for a user and document. This url allows the user
+   * to unsubscribe from a specific document without being signed in, for one-click
+   * links in emails.
+   *
+   * @param userId The user ID to unsubscribe
+   * @param documentId The document ID to unsubscribe from
+   * @returns The unsubscribe URL
+   */
+  public static unsubscribeUrl(userId: string, documentId: string) {
+    return `${env.URL}/api/subscriptions.delete?token=${this.unsubscribeToken(
+      userId,
+      documentId
+    )}&userId=${userId}&documentId=${documentId}`;
+  }
+
+  public static unsubscribeToken(userId: string, documentId: string) {
+    const hash = crypto.createHash("sha256");
+    hash.update(`${userId}-${env.SECRET_KEY}-${documentId}`);
+    return hash.digest("hex");
+  }
+}