feat(ENG-3247): add auth origin domain cookie on token creation (#4187)

* feat(ENG-3247): add auth origin domain cookie to multiple routers and update Nginx config

backend/src/server/lib/cookie.ts

@@ -0,0 +1,38 @@
+import { FastifyReply } from "fastify";
+
+import { getConfig } from "@app/lib/config/env";
+import { logger } from "@app/lib/logger";
+
+export function addAuthOriginDomainCookie(res: FastifyReply) {
+  try {
+    const appCfg = getConfig();
+
+    // Only set the cookie if the app is running in cloud mode
+    if (!appCfg.isCloud) return;
+
+    const siteUrl = appCfg.SITE_URL!;
+    let domain: string;
+
+    const { hostname } = new URL(siteUrl);
+
+    const parts = hostname.split(".");
+
+    if (parts.length >= 2) {
+      // For `app.infisical.com` => `.infisical.com`
+      domain = `.${parts.slice(-2).join(".")}`;
+    } else {
+      // If somehow only "example", fallback to itself
+      domain = `.${hostname}`;
+    }
+
+    void res.setCookie("aod", siteUrl, {
+      domain,
+      path: "/",
+      sameSite: "strict",
+      httpOnly: false,
+      secure: appCfg.HTTPS_ENABLED
+    });
+  } catch (error) {
+    logger.error(error, "Failed to set auth origin domain cookie");
+  }
+}