diff --git a/apps/backend/src/__tests__/connect.test.ts b/apps/backend/src/__tests__/connect.test.ts
index 371cec7f..2221801e 100644
--- a/apps/backend/src/__tests__/connect.test.ts
+++ b/apps/backend/src/__tests__/connect.test.ts
@@ -1,39 +1,185 @@
-import { describe, it, expect } from 'vitest';
+import Fastify, { type FastifyInstance } from 'fastify';
+import { describe, it, expect, beforeEach, vi } from 'vitest';
 
-// Mock test for GitHub OAuth callback state validation
-// Note: This test verifies the expected behavior of the
-// /api/connect/github/callback endpoint when invalid or
-// malformed OAuth state values are received.
-//
-// The implementation in connect.ts now:
-// - safely parses OAuth state via parseGoogleState()
-// - validates required fields (userId + nonce)
-// - redirects invalid callbacks safely
-//
-// Security note:
-// OAuth state validation helps prevent tampered callback
-// requests and malformed state payload attacks.
+import { connectRoutes } from '../routes/connect.js';
 
-describe('GET /api/connect/github/callback - Invalid OAuth State', () => {
+import type { PrismaClient } from '@prisma/client';
 
-    it('should redirect with connect_failed when state is invalid', async () => {
-        // Expected behavior:
-        // parseGoogleState('invalid_state') -> null
-        // reply.redirect(`${PUBLIC_APP_URL}/settings?error=connect_failed`)
+const USER_ID = 'user-abc';
+const VALID_NONCE = 'a1b2c3d4e5f6a1b2c3d4e5f6a1b2c3d4e5f6a1b2c3d4e5f6a1b2c3d4e5f6a1b2';
+const VALID_STATE = Buffer.from(JSON.stringify({ userId: USER_ID, nonce: VALID_NONCE })).toString('base64');
+const ATTACKER_USER_ID = 'user-victim';
+const CRAFTED_STATE = Buffer.from(JSON.stringify({ userId: ATTACKER_USER_ID, nonce: 'nonce-never-issued' })).toString('base64');
 
-        expect(true).toBe(true);
+// Mock encrypt so the token-storage path does not throw in tests
+vi.mock('../utils/encryption.js', () => ({
+  encrypt: vi.fn().mockReturnValue('encrypted_token'),
+}));
+
+const mockPrisma = {
+  oAuthToken: {
+    findMany: vi.fn(),
+    upsert: vi.fn(),
+    delete: vi.fn(),
+  },
+};
+
+// Redis mock that reports as connected and ready
+const mockRedis = {
+  status: 'ready',
+  set: vi.fn(),
+  get: vi.fn(),
+  del: vi.fn(),
+};
+
+// Redis mock that simulates connection failure
+const mockRedisDown = {
+  status: 'end',
+  set: vi.fn(),
+  get: vi.fn(),
+  del: vi.fn(),
+};
+
+async function buildApp(redisOverride?: object | null): Promise<FastifyInstance> {
+  const app = Fastify({ logger: false });
+  app.decorate('prisma', mockPrisma as unknown as PrismaClient);
+  app.decorate('redis', (redisOverride === undefined ? mockRedis : redisOverride) as any);
+  app.decorate('authenticate', async (request: any) => {
+    request.user = { id: USER_ID };
+  });
+  vi.stubGlobal('fetch', vi.fn().mockResolvedValue({
+    json: async () => ({ access_token: 'gh_token_abc', scope: 'user:follow' }),
+  }));
+  app.register(connectRoutes, { prefix: '/api/connect' });
+  await app.ready();
+  return app;
+}
+
+// ─────────────────────────────────────────────────────────────────────────────
+// GET /api/connect/github/callback — CSRF nonce enforcement
+// ─────────────────────────────────────────────────────────────────────────────
+
+describe('GET /api/connect/github/callback — CSRF nonce enforcement', () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    process.env.PUBLIC_APP_URL = 'https://app.devcard.test';
+    process.env.BACKEND_URL = 'https://api.devcard.test';
+    process.env.GITHUB_CLIENT_ID = 'gh_client_id';
+    process.env.GITHUB_CLIENT_SECRET = 'gh_client_secret';
+  });
+
+  it('returns 503 when Redis is unavailable (status !== ready)', async () => {
+    const app = await buildApp(mockRedisDown);
+    const res = await app.inject({
+      method: 'GET',
+      url: `/api/connect/github/callback?code=gh_code&state=${VALID_STATE}`,
+    });
+
+    expect(res.statusCode).toBe(503);
+    expect(mockPrisma.oAuthToken.upsert).not.toHaveBeenCalled();
+    expect(mockRedisDown.get).not.toHaveBeenCalled();
+  });
+
+  it('returns 503 when app.redis is null/falsy', async () => {
+    const app = await buildApp(null);
+    const res = await app.inject({
+      method: 'GET',
+      url: `/api/connect/github/callback?code=gh_code&state=${VALID_STATE}`,
+    });
+
+    expect(res.statusCode).toBe(503);
+    expect(mockPrisma.oAuthToken.upsert).not.toHaveBeenCalled();
+  });
+
+  it('redirects to invalid_state when nonce was never issued (crafted state)', async () => {
+    mockRedis.get.mockResolvedValue(null);
+
+    const app = await buildApp();
+    const res = await app.inject({
+      method: 'GET',
+      url: `/api/connect/github/callback?code=gh_code&state=${CRAFTED_STATE}`,
+    });
+
+    expect(res.statusCode).toBe(302);
+    expect(res.headers.location).toContain('error=invalid_state');
+    expect(mockPrisma.oAuthToken.upsert).not.toHaveBeenCalled();
+  });
+
+  it('redirects to invalid_state when nonce is present but userId does not match', async () => {
+    mockRedis.get.mockResolvedValue('user-different');
+
+    const app = await buildApp();
+    const res = await app.inject({
+      method: 'GET',
+      url: `/api/connect/github/callback?code=gh_code&state=${VALID_STATE}`,
+    });
+
+    expect(res.statusCode).toBe(302);
+    expect(res.headers.location).toContain('error=invalid_state');
+    expect(mockPrisma.oAuthToken.upsert).not.toHaveBeenCalled();
+  });
+
+  it('completes the OAuth flow and stores the token when nonce is valid', async () => {
+    mockRedis.get.mockResolvedValue(USER_ID);
+    mockRedis.del.mockResolvedValue(1);
+    mockPrisma.oAuthToken.upsert.mockResolvedValue({});
+
+    const app = await buildApp();
+    const res = await app.inject({
+      method: 'GET',
+      url: `/api/connect/github/callback?code=gh_code&state=${VALID_STATE}`,
     });
 
-    it('should reject malformed oauth state payloads', async () => {
-        // Example malformed payload:
-        // { invalid: true }
-        //
-        // Expected:
-        // - missing userId
-        // - missing nonce
-        // - redirect to connect_failed
+    expect(res.statusCode).toBe(302);
+    expect(res.headers.location).toContain('connected=github');
+    expect(mockRedis.del).toHaveBeenCalledWith(`oauth:nonce:${VALID_NONCE}`);
+    expect(mockPrisma.oAuthToken.upsert).toHaveBeenCalledOnce();
+  });
+
+  it('consumes the nonce exactly once — replay of the same state is rejected', async () => {
+    mockRedis.get.mockResolvedValueOnce(USER_ID);
+    mockRedis.del.mockResolvedValue(1);
+    mockPrisma.oAuthToken.upsert.mockResolvedValue({});
+
+    const app = await buildApp();
+    const first = await app.inject({
+      method: 'GET',
+      url: `/api/connect/github/callback?code=gh_code&state=${VALID_STATE}`,
+    });
+    expect(first.statusCode).toBe(302);
+    expect(first.headers.location).toContain('connected=github');
+
+    mockRedis.get.mockResolvedValueOnce(null);
+    const second = await app.inject({
+      method: 'GET',
+      url: `/api/connect/github/callback?code=gh_code&state=${VALID_STATE}`,
+    });
+    expect(second.statusCode).toBe(302);
+    expect(second.headers.location).toContain('error=invalid_state');
+    expect(mockPrisma.oAuthToken.upsert).toHaveBeenCalledOnce();
+  });
+
+  it('redirects to connect_failed when code or state is missing', async () => {
+    const app = await buildApp();
+
+    const noCode = await app.inject({ method: 'GET', url: '/api/connect/github/callback?state=abc' });
+    expect(noCode.statusCode).toBe(302);
+    expect(noCode.headers.location).toContain('error=missing_params');
+
+    const noState = await app.inject({ method: 'GET', url: '/api/connect/github/callback?code=abc' });
+    expect(noState.statusCode).toBe(302);
+    expect(noState.headers.location).toContain('error=missing_params');
+  });
 
-        expect(true).toBe(true);
+  it('redirects to connect_failed when state is not valid base64 JSON', async () => {
+    const app = await buildApp();
+    const res = await app.inject({
+      method: 'GET',
+      url: '/api/connect/github/callback?code=gh_code&state=not_valid_base64!!!',
     });
 
+    expect(res.statusCode).toBe(302);
+    expect(res.headers.location).toContain('error=connect_failed');
+    expect(mockPrisma.oAuthToken.upsert).not.toHaveBeenCalled();
+  });
 });
\ No newline at end of file
diff --git a/apps/backend/src/routes/connect.ts b/apps/backend/src/routes/connect.ts
index bb04194d..e7af79f2 100644
--- a/apps/backend/src/routes/connect.ts
+++ b/apps/backend/src/routes/connect.ts
@@ -1,7 +1,9 @@
-import type { FastifyInstance, FastifyRequest, FastifyReply } from 'fastify';
-import { randomBytes } from 'crypto';
+import { randomBytes } from 'node:crypto';
+
 import { encrypt } from '../utils/encryption.js';
 
+import type { FastifyInstance, FastifyRequest, FastifyReply } from 'fastify';
+
 const GITHUB_AUTH_URL = 'https://github.com/login/oauth/authorize';
 const GITHUB_TOKEN_URL = 'https://github.com/login/oauth/access_token';
 
@@ -30,9 +32,9 @@ export async function connectRoutes(app: FastifyInstance) {
       const server = request.server as any;
       if (typeof server?.authenticate === 'function') { await server.authenticate(request, reply); return }
       if (typeof (app as any).authenticate === 'function') { await (app as any).authenticate(request, reply); return }
-      try { await request.jwtVerify() } catch (e) { reply.status(401).send({ error: 'Unauthorized' }) }
+      try { await request.jwtVerify() } catch (_e) { reply.status(401).send({ error: 'Unauthorized' }) }
     }],
-  }, async (request: FastifyRequest, reply: FastifyReply) => {
+  }, async (request: FastifyRequest, _reply: FastifyReply) => {
     const userId = (request.user as any).id;
 
     const tokens = await app.prisma.oAuthToken.findMany({
@@ -50,7 +52,7 @@ export async function connectRoutes(app: FastifyInstance) {
       const server = request.server as any;
       if (typeof server?.authenticate === 'function') { await server.authenticate(request, reply); return }
       if (typeof (app as any).authenticate === 'function') { await (app as any).authenticate(request, reply); return }
-      try { await request.jwtVerify() } catch (e) { reply.status(401).send({ error: 'Unauthorized' }) }
+      try { await request.jwtVerify() } catch (_e) { reply.status(401).send({ error: 'Unauthorized' }) }
     }],
   }, async (request: FastifyRequest, reply: FastifyReply) => {
     const userId = (request.user as any).id;
@@ -93,16 +95,23 @@ export async function connectRoutes(app: FastifyInstance) {
         return reply.redirect(`${process.env.PUBLIC_APP_URL}/settings?error=connect_failed`);
       }
 
-      // Verify nonce was issued by this server -- prevents CSRF
-      const storedUserId = app.redis ? await app.redis.get(`oauth:nonce:${decodedState.nonce}`) : null;
+      // Hard-fail when Redis is unavailable: proceeding without nonce
+      // verification would allow CSRF — an attacker could craft a valid-looking
+      // state for any userId and have a token stored under their target's account.
+      if (!app.redis || app.redis.status !== 'ready') {
+        app.log.error('OAuth CSRF check skipped: Redis unavailable — aborting callback');
+        return reply.status(503).send({ error: 'Service temporarily unavailable. Please try again.' });
+      }
+
+      const storedUserId = await app.redis.get(`oauth:nonce:${decodedState.nonce}`);
 
-      if (app.redis && (!storedUserId || storedUserId !== decodedState.userId)) {
-        app.log.warn({ nonce: decodedState.nonce }, 'OAuth CSRF check failed: nonce mismatch');
+      if (!storedUserId || storedUserId !== decodedState.userId) {
+        app.log.warn({ nonce: decodedState.nonce }, 'OAuth CSRF check failed: nonce mismatch or nonce not found');
         return reply.redirect(`${process.env.PUBLIC_APP_URL}/settings?error=invalid_state`);
       }
 
-      // Consume the nonce -- one-time use only (if redis configured)
-      if (app.redis) await app.redis.del(`oauth:nonce:${decodedState.nonce}`);
+      // Consume the nonce — one-time use, prevents replay attacks
+      await app.redis.del(`oauth:nonce:${decodedState.nonce}`);
 
       const userId = decodedState.userId;
 
@@ -175,7 +184,7 @@ export async function connectRoutes(app: FastifyInstance) {
       const server = request.server as any;
       if (typeof server?.authenticate === 'function') { await server.authenticate(request, reply); return }
       if (typeof (app as any).authenticate === 'function') { await (app as any).authenticate(request, reply); return }
-      try { await request.jwtVerify() } catch (e) { reply.status(401).send({ error: 'Unauthorized' }) }
+      try { await request.jwtVerify() } catch (_e) { reply.status(401).send({ error: 'Unauthorized' }) }
     }],
   }, async (request: FastifyRequest<{ Params: { platform: string } }>, reply: FastifyReply) => {
     const userId = (request.user as any).id;
@@ -196,7 +205,7 @@ export async function connectRoutes(app: FastifyInstance) {
         },
       });
       return { success: true };
-    } catch (error) {
+    } catch (_error) {
       return reply.status(404).send({ error: 'Connection not found' });
     }
   });
@@ -218,4 +227,4 @@ function parseOAuthState(state: string): ParsedOAuthState | null {
 
 function generateState(): string {
   return randomBytes(32).toString('hex');
-}
+}
\ No newline at end of file