Add file cache plugin for token caching fallback in createPca function

src/azure/pca-auth.js

@@ -1,5 +1,6 @@
 
 import open, { apps } from "open";
+import fs from "node:fs";
 import path from "node:path";
 
 import { PublicClientApplication } from "@azure/msal-node";
@@ -10,20 +11,42 @@ import {
   PersistenceCreator,
 } from "@azure/msal-node-extensions";
 
+function fileCachePlugin(cachePath) {
+  return {
+    beforeCacheAccess: async (ctx) => {
+      if (fs.existsSync(cachePath)) {
+        ctx.tokenCache.deserialize(fs.readFileSync(cachePath, "utf8"));
+      }
+    },
+    afterCacheAccess: async (ctx) => {
+      if (!ctx.cacheHasChanged) return;
+      fs.mkdirSync(path.dirname(cachePath), { recursive: true });
+      fs.writeFileSync(cachePath, ctx.tokenCache.serialize());
+      fs.chmodSync(cachePath, 0o600);
+    },
+  };
+}
+
 async function createPca({ tenantId, clientId }) {
   const cacheRoot = Environment.isWindowsPlatform()
     ? path.join(Environment.getUserRootDirectory(), "sk-az-tools")
     : path.join(Environment.getUserRootDirectory(), ".config", "sk-az-tools");
 
   const cachePath = path.join(cacheRoot, `${clientId}-msal.cache`);
-
-  const persistence = await PersistenceCreator.createPersistence({
-    cachePath,
-    dataProtectionScope: DataProtectionScope.CurrentUser,
-    serviceName: "sk-az-tools",
-    accountName: "msal-cache",
-    usePlaintextFileOnLinux: true,
-  });
+  let cachePlugin;
+  try {
+    const persistence = await PersistenceCreator.createPersistence({
+      cachePath,
+      dataProtectionScope: DataProtectionScope.CurrentUser,
+      serviceName: "sk-az-tools",
+      accountName: "msal-cache",
+      usePlaintextFileOnLinux: true,
+    });
+    cachePlugin = new PersistenceCachePlugin(persistence);
+  } catch (err) {
+    // Fallback for Linux environments where libsecret integration is unavailable.
+    cachePlugin = fileCachePlugin(cachePath);
+  }
 
   return new PublicClientApplication({
     auth: {
@@ -31,7 +54,7 @@ async function createPca({ tenantId, clientId }) {
       authority: `https://login.microsoftonline.com/${tenantId}`,
     },
     cache: {
-      cachePlugin: new PersistenceCachePlugin(persistence),
+      cachePlugin,
     },
   });
 }