msal-singleton-pattern skillA
msal-singleton-pattern is agent-read markdown (skill) from fabioc-aloha/alex_skill_mall: Time Saved: 1+ hour debugging silent auth failures.
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What the file says
# MSAL Singleton Pattern
**Category**: Azure
**Time Saved**: 1+ hour debugging silent auth failures
**Battle-tested**: Yes — HeadstartWebsite, Next.js + Azure projects
---
## The Problem
Your React/Next.js app uses MSAL.js for Azure AD authentication. Login works, but token refresh fails silently. Sometimes users get logged out randomly. The console shows cryptic "interaction_in_progress" errors.
## Why It Happens
MSAL.js `PublicClientApplication` maintains an internal token cache and tracks in-flight auth requests. Creating multiple instances causes:
- Token cache conflicts (different instances don't share tokens)
- Race conditions on `acquireTokenSilent`
- "interaction_in_progress" errors when two instances try to redirect
## The Rule
**Initialize MSAL once, share the singleton across your entire app**
```typescript
// ❌ BROKEN — new instance on every import/render
function getAuth() {
return new PublicClientApplication(msalConfig);
}
// ✅ CORRECT — module-level singleton with async init
let msalInstance: PublicClientApplication | null = null;
let initPromise: Promise<PublicClientApplication> | null = null;
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How to install
mdr add fabioc-aloha/alex_skill_mall/msal-singleton-pattern@git:20260728.80a7ab6mdr add fabioc-aloha/alex_skill_mall/msal-singleton-pattern@sha256:a4b2ab786562abd8Pin to a label to follow the author's releases, or to a sha256 to freeze the exact bytes forever. Either way the resolved hash is written to mdr.lock, and mdr install reproduces it on any machine.
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Source
fabioc-aloha/alex_skill_mall · 4 stars · license MIT · pushed 2026-09-21 · branch main
API
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