Simple SSO feature for login flows from external services (#2553)

* Simple SSO feature for login flows from external services

* linting

server/utils/middleware/simpleSSOEnabled.js

@@ -0,0 +1,39 @@
+const { SystemSettings } = require("../../models/systemSettings");
+
+/**
+ * Checks if simple SSO is enabled for issuance of temporary auth tokens.
+ * Note: This middleware must be called after `validApiKey`.
+ * @param {import("express").Request} request
+ * @param {import("express").Response} response
+ * @param {import("express").NextFunction} next
+ * @returns {void}
+ */
+async function simpleSSOEnabled(_, response, next) {
+  if (!("SIMPLE_SSO_ENABLED" in process.env)) {
+    return response
+      .status(403)
+      .send(
+        "Simple SSO is not enabled. It must be enabled to validate or issue temporary auth tokens."
+      );
+  }
+
+  // If the multi-user mode response local is not set, we need to check if it's enabled.
+  if (!("multiUserMode" in response.locals)) {
+    const multiUserMode = await SystemSettings.isMultiUserMode();
+    response.locals.multiUserMode = multiUserMode;
+  }
+
+  if (!response.locals.multiUserMode) {
+    return response
+      .status(403)
+      .send(
+        "Multi-User mode is not enabled. It must be enabled to use Simple SSO."
+      );
+  }
+
+  next();
+}
+
+module.exports = {
+  simpleSSOEnabled,
+};