diff --git a/app/(auth)/login/page.tsx b/app/(auth)/login/page.tsx
index f61eef60..b0ccbac0 100644
--- a/app/(auth)/login/page.tsx
+++ b/app/(auth)/login/page.tsx
@@ -1,6 +1,6 @@
 'use client'
 
-import { useState } from 'react'
+import { useState, useEffect } from 'react'
 import { useRouter } from 'next/navigation'
 import Link from 'next/link'
 import { createClient } from '@/lib/supabase/client'
@@ -18,10 +18,25 @@ export default function LoginPage() {
   const [isLoading, setIsLoading] = useState(false)
   const [isEmailSent, setIsEmailSent] = useState(false)
   const [showResetPassword, setShowResetPassword] = useState(false)
+  const [resetCooldownUntil, setResetCooldownUntil] = useState<number | null>(null)
+  const [resetCooldownRemaining, setResetCooldownRemaining] = useState(0)
   const { toast } = useToast()
   const router = useRouter()
   const supabase = createClient()
 
+  // Reset cooldown timer
+  useEffect(() => {
+    if (!resetCooldownUntil) return
+    const tick = () => {
+      const remaining = Math.max(0, Math.ceil((resetCooldownUntil - Date.now()) / 1000))
+      setResetCooldownRemaining(remaining)
+      if (remaining <= 0) setResetCooldownUntil(null)
+    }
+    tick()
+    const interval = setInterval(tick, 1000)
+    return () => clearInterval(interval)
+  }, [resetCooldownUntil])
+
   const handlePasswordLogin = async (e: React.FormEvent<HTMLFormElement>) => {
     e.preventDefault()
     setIsLoading(true)
@@ -31,27 +46,12 @@ export default function LoginPage() {
     const passwordValue = (formData.get('password') as string) || password
 
     try {
-      console.log('[login] attempting signInWithPassword', {
-        email: emailValue,
-        hasPassword: !!passwordValue,
-        supabaseUrl: process.env.NEXT_PUBLIC_SUPABASE_URL,
-      })
-
-      const { data, error } = await supabase.auth.signInWithPassword({
+      const { error } = await supabase.auth.signInWithPassword({
         email: emailValue,
         password: passwordValue,
       })
 
       if (error) {
-        console.error('[login] signInWithPassword error', {
-          message: error.message,
-          code: error.code,
-          status: error.status,
-          name: error.name,
-          stack: error.stack,
-          cause: error.cause,
-          fullError: JSON.stringify(error, Object.getOwnPropertyNames(error)),
-        })
         toast({
           title: 'Inloggning misslyckades',
           description: error.message === 'Invalid login credentials'
@@ -62,24 +62,8 @@ export default function LoginPage() {
         return
       }
 
-      console.log('[login] signInWithPassword success', {
-        userId: data.user?.id,
-        email: data.user?.email,
-        hasSession: !!data.session,
-        provider: data.user?.app_metadata?.provider,
-      })
-
       // Check MFA status
-      const { data: aal, error: mfaError } = await supabase.auth.mfa.getAuthenticatorAssuranceLevel()
-      if (mfaError) {
-        console.error('[login] MFA check error', {
-          message: mfaError.message,
-          code: mfaError.code,
-          status: mfaError.status,
-          fullError: JSON.stringify(mfaError, Object.getOwnPropertyNames(mfaError)),
-        })
-      }
-      console.log('[login] MFA status', { currentLevel: aal?.currentLevel, nextLevel: aal?.nextLevel })
+      const { data: aal } = await supabase.auth.mfa.getAuthenticatorAssuranceLevel()
 
       if (aal?.nextLevel === 'aal2' && aal?.currentLevel === 'aal1') {
         router.push('/mfa/verify')
@@ -89,13 +73,6 @@ export default function LoginPage() {
       router.push('/')
       router.refresh()
     } catch (error) {
-      console.error('[login] unexpected exception', {
-        error,
-        message: error instanceof Error ? error.message : String(error),
-        stack: error instanceof Error ? error.stack : undefined,
-        type: typeof error,
-        constructor: error?.constructor?.name,
-      })
       toast({
         title: 'Inloggning misslyckades',
         description: getErrorMessage(error, { context: 'auth' }),
@@ -114,25 +91,11 @@ export default function LoginPage() {
     const emailValue = (formData.get('email') as string) || email
 
     try {
-      console.log('[login] attempting resetPasswordForEmail', {
-        email: emailValue,
-        redirectTo: `${window.location.origin}/auth/callback?next=/reset-password`,
-      })
-
       const { error } = await supabase.auth.resetPasswordForEmail(emailValue, {
         redirectTo: `${window.location.origin}/auth/callback?next=/reset-password`,
       })
 
       if (error) {
-        console.error('[login] resetPasswordForEmail error', {
-          message: error.message,
-          code: error.code,
-          status: error.status,
-          name: error.name,
-          stack: error.stack,
-          cause: error.cause,
-          fullError: JSON.stringify(error, Object.getOwnPropertyNames(error)),
-        })
         toast({
           title: 'Kunde inte skicka återställningslänk',
           description: getErrorMessage(error, { context: 'auth' }),
@@ -141,21 +104,14 @@ export default function LoginPage() {
         return
       }
 
-      console.log('[login] resetPasswordForEmail success', { email: emailValue })
       setEmail(emailValue)
+      setResetCooldownUntil(Date.now() + 60_000)
       setIsEmailSent(true)
       toast({
         title: 'Återställningslänk skickad!',
         description: 'Kolla din inkorg för att återställa lösenordet.',
       })
     } catch (error) {
-      console.error('[login] resetPasswordForEmail unexpected exception', {
-        error,
-        message: error instanceof Error ? error.message : String(error),
-        stack: error instanceof Error ? error.stack : undefined,
-        type: typeof error,
-        constructor: error?.constructor?.name,
-      })
       toast({
         title: 'Kunde inte skicka återställningslänk',
         description: getErrorMessage(error, { context: 'auth' }),
@@ -242,12 +198,14 @@ export default function LoginPage() {
                   className="h-11"
                 />
               </div>
-              <Button type="submit" className="w-full h-11" disabled={isLoading}>
+              <Button type="submit" className="w-full h-11" disabled={isLoading || !!resetCooldownUntil}>
                 {isLoading ? (
                   <>
                     <Loader2 className="mr-2 h-4 w-4 animate-spin" />
                     Skickar...
                   </>
+                ) : resetCooldownUntil ? (
+                  `Vänta ${resetCooldownRemaining}s`
                 ) : (
                   'Skicka återställningslänk'
                 )}
diff --git a/app/(auth)/mfa/verify/page.tsx b/app/(auth)/mfa/verify/page.tsx
index 45d8112e..1e4789d6 100644
--- a/app/(auth)/mfa/verify/page.tsx
+++ b/app/(auth)/mfa/verify/page.tsx
@@ -14,6 +14,9 @@ export default function MfaVerifyPage() {
   const [code, setCode] = useState('')
   const [isLoading, setIsLoading] = useState(false)
   const [factorId, setFactorId] = useState<string | null>(null)
+  const [failedAttempts, setFailedAttempts] = useState(0)
+  const [lockoutUntil, setLockoutUntil] = useState<number | null>(null)
+  const [lockoutRemaining, setLockoutRemaining] = useState(0)
   const inputRef = useRef<HTMLInputElement>(null)
   const { toast } = useToast()
   const router = useRouter()
@@ -35,6 +38,19 @@ export default function MfaVerifyPage() {
     // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [])
 
+  // Lockout countdown timer
+  useEffect(() => {
+    if (!lockoutUntil) return
+    const tick = () => {
+      const remaining = Math.max(0, Math.ceil((lockoutUntil - Date.now()) / 1000))
+      setLockoutRemaining(remaining)
+      if (remaining <= 0) setLockoutUntil(null)
+    }
+    tick()
+    const interval = setInterval(tick, 1000)
+    return () => clearInterval(interval)
+  }, [lockoutUntil])
+
   const handleVerify = async (e: React.FormEvent<HTMLFormElement>) => {
     e.preventDefault()
     if (!factorId || code.length !== 6) return
@@ -63,6 +79,16 @@ export default function MfaVerifyPage() {
       })
 
       if (verifyError) {
+        const attempts = failedAttempts + 1
+        setFailedAttempts(attempts)
+
+        // Exponential backoff after 3 failed attempts: 5s, 15s, 30s
+        if (attempts >= 3) {
+          const delays = [5_000, 15_000, 30_000]
+          const delay = delays[Math.min(attempts - 3, delays.length - 1)]
+          setLockoutUntil(Date.now() + delay)
+        }
+
         toast({
           title: 'Fel kod',
           description: 'Kontrollera koden och försök igen.',
@@ -130,13 +156,15 @@ export default function MfaVerifyPage() {
             <Button
               type="submit"
               className="w-full h-11"
-              disabled={isLoading || code.length !== 6}
+              disabled={isLoading || code.length !== 6 || !!lockoutUntil}
             >
               {isLoading ? (
                 <>
                   <Loader2 className="mr-2 h-4 w-4 animate-spin" />
                   Verifierar...
                 </>
+              ) : lockoutUntil ? (
+                `Vänta ${lockoutRemaining}s`
               ) : (
                 'Verifiera'
               )}
diff --git a/app/api/admin/seed-template-embeddings/route.ts b/app/api/admin/seed-template-embeddings/route.ts
index e39b174f..af8d4697 100644
--- a/app/api/admin/seed-template-embeddings/route.ts
+++ b/app/api/admin/seed-template-embeddings/route.ts
@@ -1,16 +1,13 @@
 import { NextResponse } from 'next/server'
 import { extensionRegistry } from '@/lib/extensions/registry'
 import { ensureInitialized } from '@/lib/init'
+import { verifyCronSecret } from '@/lib/auth/cron'
 
 ensureInitialized()
 
 export async function POST(request: Request) {
-  const authHeader = request.headers.get('authorization')
-  const cronSecret = process.env.CRON_SECRET
-
-  if (!cronSecret || authHeader !== `Bearer ${cronSecret}`) {
-    return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
-  }
+  const authError = verifyCronSecret(request)
+  if (authError) return authError
 
   const aiExt = extensionRegistry.get('ai-categorization')
   if (!aiExt?.services?.seedAllTemplateEmbeddings || !aiExt?.services?.getSchemaVersion) {
diff --git a/app/api/calendar/feed/[token]/route.ts b/app/api/calendar/feed/[token]/route.ts
index 7ed20d24..46e60c64 100644
--- a/app/api/calendar/feed/[token]/route.ts
+++ b/app/api/calendar/feed/[token]/route.ts
@@ -2,6 +2,22 @@ import { createClient } from '@supabase/supabase-js'
 import { NextResponse } from 'next/server'
 import { generateCalendarFeed } from '@/lib/calendar/ics-generator'
 
+// In-memory rate limiting: token -> { count, resetAt }
+const rateLimitMap = new Map<string, { count: number; resetAt: number }>()
+const RATE_LIMIT_WINDOW_MS = 60_000 // 1 minute
+const RATE_LIMIT_MAX = 60 // 60 requests per minute per token
+
+// Periodic cleanup to prevent memory leaks (every 5 minutes)
+let lastCleanup = Date.now()
+function cleanupRateLimitMap() {
+  const now = Date.now()
+  if (now - lastCleanup < 5 * 60_000) return
+  lastCleanup = now
+  for (const [key, value] of rateLimitMap) {
+    if (now > value.resetAt) rateLimitMap.delete(key)
+  }
+}
+
 /**
  * GET /api/calendar/feed/[token]
  * Returns an ICS calendar feed for the given token
@@ -19,6 +35,19 @@ export async function GET(
     return new NextResponse('Invalid token', { status: 400 })
   }
 
+  // Rate limiting per token
+  cleanupRateLimitMap()
+  const nowMs = Date.now()
+  const rateEntry = rateLimitMap.get(token)
+  if (rateEntry && nowMs < rateEntry.resetAt) {
+    if (rateEntry.count >= RATE_LIMIT_MAX) {
+      return new NextResponse('Too many requests', { status: 429 })
+    }
+    rateEntry.count++
+  } else {
+    rateLimitMap.set(token, { count: 1, resetAt: nowMs + RATE_LIMIT_WINDOW_MS })
+  }
+
   // Create service client (no user auth required)
   const supabaseUrl = process.env.NEXT_PUBLIC_SUPABASE_URL
   const supabaseServiceKey = process.env.SUPABASE_SERVICE_ROLE_KEY
@@ -41,6 +70,11 @@ export async function GET(
     return new NextResponse('Feed not found or inactive', { status: 404 })
   }
 
+  // Check token expiry
+  if (feed.expires_at && new Date(feed.expires_at) < new Date()) {
+    return new NextResponse('Feed token has expired', { status: 410 })
+  }
+
   // Update access tracking
   await supabase
     .from('calendar_feeds')
diff --git a/app/api/deadlines/status/cron/route.ts b/app/api/deadlines/status/cron/route.ts
index ec739748..aaa7c9d7 100644
--- a/app/api/deadlines/status/cron/route.ts
+++ b/app/api/deadlines/status/cron/route.ts
@@ -1,6 +1,7 @@
 import { createClient } from '@supabase/supabase-js'
 import { NextResponse } from 'next/server'
 import { updateDeadlineStatuses } from '@/lib/deadlines/status-engine'
+import { verifyCronSecret } from '@/lib/auth/cron'
 
 /**
  * GET /api/deadlines/status/cron
@@ -10,13 +11,8 @@ import { updateDeadlineStatuses } from '@/lib/deadlines/status-engine'
  * Vercel Cron: "0 6 * * *"
  */
 export async function GET(request: Request) {
-  // Verify cron secret for security
-  const authHeader = request.headers.get('authorization')
-  const cronSecret = process.env.CRON_SECRET
-
-  if (!cronSecret || authHeader !== `Bearer ${cronSecret}`) {
-    return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
-  }
+  const authError = verifyCronSecret(request)
+  if (authError) return authError
 
   // Create a service role client for accessing all user data
   const supabaseUrl = process.env.NEXT_PUBLIC_SUPABASE_URL
diff --git a/app/api/documents/verify/cron/route.ts b/app/api/documents/verify/cron/route.ts
index 5ba67933..e69b23d5 100644
--- a/app/api/documents/verify/cron/route.ts
+++ b/app/api/documents/verify/cron/route.ts
@@ -1,5 +1,6 @@
 import { createClient } from '@supabase/supabase-js'
 import { NextResponse } from 'next/server'
+import { verifyCronSecret } from '@/lib/auth/cron'
 
 /**
  * GET /api/documents/verify/cron
@@ -12,13 +13,8 @@ import { NextResponse } from 'next/server'
  * Uses service role for cross-user verification (RLS bypass).
  */
 export async function GET(request: Request) {
-  // Verify cron secret
-  const authHeader = request.headers.get('authorization')
-  const cronSecret = process.env.CRON_SECRET
-
-  if (!cronSecret || authHeader !== `Bearer ${cronSecret}`) {
-    return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
-  }
+  const authError = verifyCronSecret(request)
+  if (authError) return authError
 
   const supabaseUrl = process.env.NEXT_PUBLIC_SUPABASE_URL
   const supabaseServiceKey = process.env.SUPABASE_SERVICE_ROLE_KEY
diff --git a/app/api/extensions/enable-banking/callback/route.ts b/app/api/extensions/enable-banking/callback/route.ts
index aada6ad4..4f35435c 100644
--- a/app/api/extensions/enable-banking/callback/route.ts
+++ b/app/api/extensions/enable-banking/callback/route.ts
@@ -69,6 +69,12 @@ export async function GET(request: Request) {
     return NextResponse.redirect(`${baseUrl}/settings?bank_error=missing_parameters`)
   }
 
+  // Validate authorization code format
+  const codePattern = /^[a-zA-Z0-9._~+\/-]{8,2048}$/
+  if (!codePattern.test(code)) {
+    return NextResponse.redirect(`${baseUrl}/settings?bank_error=invalid_code_format`)
+  }
+
   const supabase = await createServiceClient()
 
   try {
@@ -105,7 +111,7 @@ export async function GET(request: Request) {
 
     console.log('[enable-banking] Session created successfully', {
       connectionId: pendingConnection.id,
-      sessionId: session_id,
+      sessionId: '[REDACTED]',
       accountCount: accounts.length,
       consentExpiresAt,
     })
@@ -150,7 +156,7 @@ export async function GET(request: Request) {
       console.error('[enable-banking] Failed to update connection after session creation', {
         connectionId: pendingConnection.id,
         updateError: { message: updateError.message, code: updateError.code, details: updateError.details },
-        sessionId: session_id,
+        sessionId: '[REDACTED]',
       })
       throw new Error(`Failed to update connection: ${updateError.message}`)
     }
diff --git a/app/api/extensions/enable-banking/sync/cron/route.ts b/app/api/extensions/enable-banking/sync/cron/route.ts
index 6c260064..81df6ee7 100644
--- a/app/api/extensions/enable-banking/sync/cron/route.ts
+++ b/app/api/extensions/enable-banking/sync/cron/route.ts
@@ -10,6 +10,7 @@ import {
   generateConsentExpiryEmailSubject,
 } from '@/lib/email/consent-notification-templates'
 import { ensureInitialized } from '@/lib/init'
+import { verifyCronSecret } from '@/lib/auth/cron'
 import type { StoredAccount } from '@/extensions/general/enable-banking/types'
 
 ensureInitialized()
@@ -24,13 +25,8 @@ ensureInitialized()
  * Deduplication via external_id makes repeated runs safe.
  */
 export async function GET(request: Request) {
-  // Verify cron secret
-  const authHeader = request.headers.get('authorization')
-  const cronSecret = process.env.CRON_SECRET
-
-  if (!cronSecret || authHeader !== `Bearer ${cronSecret}`) {
-    return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
-  }
+  const authError = verifyCronSecret(request)
+  if (authError) return authError
 
   const supabaseUrl = process.env.NEXT_PUBLIC_SUPABASE_URL
   const supabaseServiceKey = process.env.SUPABASE_SERVICE_ROLE_KEY
@@ -212,7 +208,7 @@ export async function GET(request: Request) {
         connectionId: connection.id,
         userId: connection.user_id,
         bankName: connection.bank_name,
-        sessionId: connection.session_id,
+        sessionId: '[REDACTED]',
         consentExpires: connection.consent_expires,
         lastSyncedAt: connection.last_synced_at,
         message,
diff --git a/app/api/invoices/reminders/cron/route.ts b/app/api/invoices/reminders/cron/route.ts
index 2efb97ae..5ac84d76 100644
--- a/app/api/invoices/reminders/cron/route.ts
+++ b/app/api/invoices/reminders/cron/route.ts
@@ -1,34 +1,11 @@
 import { NextResponse } from 'next/server'
 import { processOverdueReminders } from '@/lib/invoices/reminder-processor'
 import { getEmailService } from '@/lib/email/service'
-
-// Verify cron secret for security
-function verifyCronSecret(request: Request): boolean {
-  const authHeader = request.headers.get('authorization')
-  const cronSecret = process.env.CRON_SECRET
-
-  if (!cronSecret) {
-    console.error('CRON_SECRET not configured')
-    return false
-  }
-
-  if (!authHeader) {
-    return false
-  }
-
-  // Support both "Bearer <token>" and just "<token>" formats
-  const token = authHeader.startsWith('Bearer ')
-    ? authHeader.substring(7)
-    : authHeader
-
-  return token === cronSecret
-}
+import { verifyCronSecret } from '@/lib/auth/cron'
 
 export async function GET(request: Request) {
-  // Verify cron authentication
-  if (!verifyCronSecret(request)) {
-    return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
-  }
+  const authError = verifyCronSecret(request)
+  if (authError) return authError
 
   // Check if email service is configured
   if (!getEmailService().isConfigured()) {
diff --git a/app/api/mcp-oauth/register/__tests__/route.test.ts b/app/api/mcp-oauth/register/__tests__/route.test.ts
new file mode 100644
index 00000000..d13c884a
--- /dev/null
+++ b/app/api/mcp-oauth/register/__tests__/route.test.ts
@@ -0,0 +1,88 @@
+import { describe, it, expect } from 'vitest'
+import { POST } from '../route'
+
+function createRequest(body: unknown) {
+  return new Request('http://localhost/api/mcp-oauth/register', {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify(body),
+  })
+}
+
+describe('POST /api/mcp-oauth/register', () => {
+  it('returns 400 for invalid JSON', async () => {
+    const request = new Request('http://localhost/api/mcp-oauth/register', {
+      method: 'POST',
+      body: 'not json',
+    })
+    const response = await POST(request)
+    expect(response.status).toBe(400)
+  })
+
+  it('accepts registration with valid claude.ai redirect_uris', async () => {
+    const response = await POST(createRequest({
+      client_name: 'Test Client',
+      redirect_uris: ['https://claude.ai/api/oauth/callback'],
+    }))
+    expect(response.status).toBe(201)
+    const body = await response.json()
+    expect(body.client_id).toBeDefined()
+    expect(body.redirect_uris).toEqual(['https://claude.ai/api/oauth/callback'])
+  })
+
+  it('accepts registration with localhost redirect_uris', async () => {
+    const response = await POST(createRequest({
+      redirect_uris: ['http://localhost:3000/callback'],
+    }))
+    expect(response.status).toBe(201)
+  })
+
+  it('accepts registration with 127.0.0.1 redirect_uris', async () => {
+    const response = await POST(createRequest({
+      redirect_uris: ['http://127.0.0.1:8080/callback'],
+    }))
+    expect(response.status).toBe(201)
+  })
+
+  it('accepts registration with claude.com redirect_uris', async () => {
+    const response = await POST(createRequest({
+      redirect_uris: ['https://claude.com/api/oauth/callback'],
+    }))
+    expect(response.status).toBe(201)
+  })
+
+  it('rejects registration with disallowed redirect_uris', async () => {
+    const response = await POST(createRequest({
+      redirect_uris: ['https://evil.com/callback'],
+    }))
+    expect(response.status).toBe(400)
+    const body = await response.json()
+    expect(body.error).toBe('invalid_redirect_uri')
+  })
+
+  it('rejects if any redirect_uri in array is invalid', async () => {
+    const response = await POST(createRequest({
+      redirect_uris: [
+        'https://claude.ai/api/callback',
+        'https://evil.com/steal',
+      ],
+    }))
+    expect(response.status).toBe(400)
+  })
+
+  it('accepts registration with no redirect_uris', async () => {
+    const response = await POST(createRequest({
+      client_name: 'No URIs',
+    }))
+    expect(response.status).toBe(201)
+    const body = await response.json()
+    expect(body.redirect_uris).toEqual([])
+  })
+
+  it('defaults client_name to MCP Client', async () => {
+    const response = await POST(createRequest({}))
+    expect(response.status).toBe(201)
+    const body = await response.json()
+    expect(body.client_name).toBe('MCP Client')
+  })
+})
diff --git a/app/api/mcp-oauth/register/route.ts b/app/api/mcp-oauth/register/route.ts
index f24a5231..198889ca 100644
--- a/app/api/mcp-oauth/register/route.ts
+++ b/app/api/mcp-oauth/register/route.ts
@@ -1,10 +1,22 @@
 import { NextResponse } from 'next/server'
 import crypto from 'crypto'
 
+// Allowed redirect URI patterns (must match CLAUDE.md allowlist)
+const ALLOWED_REDIRECT_PATTERNS = [
+  /^https:\/\/claude\.ai\/api\//,
+  /^https:\/\/claude\.com\/api\//,
+  /^http:\/\/localhost(:\d+)?(\/|$)/,
+  /^http:\/\/127\.0\.0\.1(:\d+)?(\/|$)/,
+]
+
+function isRedirectUriAllowed(uri: string): boolean {
+  return ALLOWED_REDIRECT_PATTERNS.some(pattern => pattern.test(uri))
+}
+
 /**
  * RFC 7591 — Dynamic Client Registration.
  * Claude Desktop registers itself as an OAuth client before starting the auth flow.
- * We accept any registration and return a client_id.
+ * Validates redirect_uris against the allowlist before accepting registration.
  */
 export async function POST(request: Request) {
   let body: Record<string, unknown>
@@ -14,12 +26,23 @@ export async function POST(request: Request) {
     return NextResponse.json({ error: 'invalid_request' }, { status: 400 })
   }
 
+  // Validate redirect_uris against allowlist
+  const redirectUris = Array.isArray(body.redirect_uris) ? body.redirect_uris : []
+  for (const uri of redirectUris) {
+    if (typeof uri !== 'string' || !isRedirectUriAllowed(uri)) {
+      return NextResponse.json(
+        { error: 'invalid_redirect_uri', error_description: `Redirect URI not allowed: ${uri}` },
+        { status: 400 }
+      )
+    }
+  }
+
   const clientId = crypto.randomUUID()
 
   return NextResponse.json({
     client_id: clientId,
     client_name: (body.client_name as string) || 'MCP Client',
-    redirect_uris: body.redirect_uris || [],
+    redirect_uris: redirectUris,
     grant_types: ['authorization_code'],
     response_types: ['code'],
     token_endpoint_auth_method: 'none',
diff --git a/app/api/sandbox/cleanup/cron/route.ts b/app/api/sandbox/cleanup/cron/route.ts
index 2153acff..3a59ec40 100644
--- a/app/api/sandbox/cleanup/cron/route.ts
+++ b/app/api/sandbox/cleanup/cron/route.ts
@@ -1,5 +1,6 @@
 import { createClient } from '@supabase/supabase-js'
 import { NextResponse } from 'next/server'
+import { verifyCronSecret } from '@/lib/auth/cron'
 
 /**
  * GET /api/sandbox/cleanup/cron
@@ -7,12 +8,8 @@ import { NextResponse } from 'next/server'
  * Runs at 04:00 UTC every day.
  */
 export async function GET(request: Request) {
-  const authHeader = request.headers.get('authorization')
-  const cronSecret = process.env.CRON_SECRET
-
-  if (!cronSecret || authHeader !== `Bearer ${cronSecret}`) {
-    return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
-  }
+  const authError = verifyCronSecret(request)
+  if (authError) return authError
 
   const supabaseUrl = process.env.NEXT_PUBLIC_SUPABASE_URL
   const supabaseServiceKey = process.env.SUPABASE_SERVICE_ROLE_KEY
diff --git a/app/api/tax-deadlines/cron/route.ts b/app/api/tax-deadlines/cron/route.ts
index 0326b6ee..e7c282a3 100644
--- a/app/api/tax-deadlines/cron/route.ts
+++ b/app/api/tax-deadlines/cron/route.ts
@@ -1,6 +1,7 @@
 import { createClient } from '@supabase/supabase-js'
 import { NextResponse } from 'next/server'
 import { generateNewYearDeadlines } from '@/lib/tax/deadline-generator'
+import { verifyCronSecret } from '@/lib/auth/cron'
 
 /**
  * GET /api/tax-deadlines/cron
@@ -10,13 +11,8 @@ import { generateNewYearDeadlines } from '@/lib/tax/deadline-generator'
  * Vercel Cron: "0 0 2 1 *" (midnight on January 2nd)
  */
 export async function GET(request: Request) {
-  // Verify cron secret for security
-  const authHeader = request.headers.get('authorization')
-  const cronSecret = process.env.CRON_SECRET
-
-  if (!cronSecret || authHeader !== `Bearer ${cronSecret}`) {
-    return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
-  }
+  const authError = verifyCronSecret(request)
+  if (authError) return authError
 
   // Create a service role client for accessing all user data
   const supabaseUrl = process.env.NEXT_PUBLIC_SUPABASE_URL
diff --git a/lib/auth/__tests__/cron.test.ts b/lib/auth/__tests__/cron.test.ts
new file mode 100644
index 00000000..781a2c02
--- /dev/null
+++ b/lib/auth/__tests__/cron.test.ts
@@ -0,0 +1,64 @@
+import { describe, it, expect, beforeEach, vi } from 'vitest'
+import { verifyCronSecret } from '../cron'
+
+describe('verifyCronSecret', () => {
+  beforeEach(() => {
+    vi.unstubAllEnvs()
+  })
+
+  it('returns 401 when CRON_SECRET is not set', () => {
+    vi.stubEnv('CRON_SECRET', '')
+    const request = new Request('http://localhost/api/cron', {
+      headers: { authorization: 'Bearer test-secret' },
+    })
+    const result = verifyCronSecret(request)
+    expect(result).not.toBeNull()
+    expect(result!.status).toBe(401)
+  })
+
+  it('returns 401 when no authorization header is provided', () => {
+    vi.stubEnv('CRON_SECRET', 'test-secret')
+    const request = new Request('http://localhost/api/cron')
+    const result = verifyCronSecret(request)
+    expect(result).not.toBeNull()
+    expect(result!.status).toBe(401)
+  })
+
+  it('returns 401 when token does not match', () => {
+    vi.stubEnv('CRON_SECRET', 'correct-secret')
+    const request = new Request('http://localhost/api/cron', {
+      headers: { authorization: 'Bearer wrong-secret' },
+    })
+    const result = verifyCronSecret(request)
+    expect(result).not.toBeNull()
+    expect(result!.status).toBe(401)
+  })
+
+  it('returns null (authorized) when Bearer token matches', () => {
+    vi.stubEnv('CRON_SECRET', 'correct-secret')
+    const request = new Request('http://localhost/api/cron', {
+      headers: { authorization: 'Bearer correct-secret' },
+    })
+    const result = verifyCronSecret(request)
+    expect(result).toBeNull()
+  })
+
+  it('returns null (authorized) when bare token matches', () => {
+    vi.stubEnv('CRON_SECRET', 'correct-secret')
+    const request = new Request('http://localhost/api/cron', {
+      headers: { authorization: 'correct-secret' },
+    })
+    const result = verifyCronSecret(request)
+    expect(result).toBeNull()
+  })
+
+  it('handles tokens of different lengths safely', () => {
+    vi.stubEnv('CRON_SECRET', 'short')
+    const request = new Request('http://localhost/api/cron', {
+      headers: { authorization: 'Bearer a-much-longer-token-that-differs-in-length' },
+    })
+    const result = verifyCronSecret(request)
+    expect(result).not.toBeNull()
+    expect(result!.status).toBe(401)
+  })
+})
diff --git a/lib/auth/cron.ts b/lib/auth/cron.ts
new file mode 100644
index 00000000..ceabc970
--- /dev/null
+++ b/lib/auth/cron.ts
@@ -0,0 +1,32 @@
+import crypto from 'crypto'
+import { NextResponse } from 'next/server'
+
+/**
+ * Verify cron secret using constant-time comparison to prevent timing attacks.
+ * Expects `Authorization: Bearer <CRON_SECRET>` header.
+ *
+ * Returns null if authorized, or a 401 NextResponse if not.
+ */
+export function verifyCronSecret(request: Request): NextResponse | null {
+  const authHeader = request.headers.get('authorization')
+  const cronSecret = process.env.CRON_SECRET
+
+  if (!cronSecret || !authHeader) {
+    return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
+  }
+
+  const token = authHeader.startsWith('Bearer ')
+    ? authHeader.substring(7)
+    : authHeader
+
+  // Use timingSafeEqual to prevent timing-based secret extraction.
+  // Encode both to buffers of equal length by hashing with SHA-256.
+  const tokenHash = crypto.createHash('sha256').update(token).digest()
+  const secretHash = crypto.createHash('sha256').update(cronSecret).digest()
+
+  if (!crypto.timingSafeEqual(tokenHash, secretHash)) {
+    return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
+  }
+
+  return null
+}
diff --git a/supabase/migrations/20260329120000_calendar_feed_expiry.sql b/supabase/migrations/20260329120000_calendar_feed_expiry.sql
new file mode 100644
index 00000000..623701cf
--- /dev/null
+++ b/supabase/migrations/20260329120000_calendar_feed_expiry.sql
@@ -0,0 +1,6 @@
+-- Add optional expiry to calendar feed tokens
+-- Null = no expiry (preserves existing tokens)
+ALTER TABLE calendar_feeds
+  ADD COLUMN IF NOT EXISTS expires_at TIMESTAMPTZ DEFAULT NULL;
+
+COMMENT ON COLUMN calendar_feeds.expires_at IS 'Optional token expiry. Null means the token never expires.';