diff --git a/src/app/api/auth/calendars/route.ts b/src/app/api/auth/calendars/route.ts
new file mode 100644
index 0000000..787ce4f
--- /dev/null
+++ b/src/app/api/auth/calendars/route.ts
@@ -0,0 +1,45 @@
+import { NextRequest, NextResponse } from 'next/server'
+import { requireAuth, isAuthed } from '@/lib/auth'
+import { prisma } from '@/lib/prisma'
+
+/**
+ * GET /api/auth/calendars
+ * Returns the authenticated user's calendar sources from the DB.
+ * Note: OAuth tokens are stored client-side (encrypted by EncryptID),
+ * so this only returns source metadata — never credentials.
+ */
+export async function GET(request: NextRequest) {
+  try {
+    const auth = await requireAuth(request)
+    if (!isAuthed(auth)) return auth
+
+    const sources = await prisma.calendarSource.findMany({
+      where: { createdById: auth.user.id },
+      select: {
+        id: true,
+        name: true,
+        sourceType: true,
+        color: true,
+        isActive: true,
+        lastSyncedAt: true,
+        syncError: true,
+      },
+      orderBy: { createdAt: 'desc' },
+    })
+
+    return NextResponse.json({
+      sources: sources.map((s: typeof sources[number]) => ({
+        id: s.id,
+        name: s.name,
+        provider: s.sourceType,
+        color: s.color,
+        is_active: s.isActive,
+        last_synced_at: s.lastSyncedAt?.toISOString() || null,
+        has_error: !!s.syncError,
+      })),
+    })
+  } catch (err) {
+    console.error('Connected calendars error:', err)
+    return NextResponse.json({ error: 'Failed to fetch connected calendars' }, { status: 500 })
+  }
+}
diff --git a/src/app/api/auth/google/authorize/route.ts b/src/app/api/auth/google/authorize/route.ts
new file mode 100644
index 0000000..40ed099
--- /dev/null
+++ b/src/app/api/auth/google/authorize/route.ts
@@ -0,0 +1,48 @@
+import { NextRequest, NextResponse } from 'next/server'
+import { requireAuth, isAuthed } from '@/lib/auth'
+import { buildGoogleAuthUrl, generateStateToken } from '@/lib/oauth'
+import { cookies } from 'next/headers'
+
+/**
+ * GET /api/auth/google/authorize
+ * Generates a Google OAuth URL and redirects the user.
+ * CSRF protection via a state token stored in a secure httpOnly cookie.
+ */
+export async function GET(request: NextRequest) {
+  try {
+    const auth = await requireAuth(request)
+    if (!isAuthed(auth)) return auth
+
+    const stateToken = generateStateToken()
+
+    // Store state + user ID in a secure, httpOnly, short-lived cookie
+    const statePayload = JSON.stringify({
+      csrf: stateToken,
+      userId: auth.user.id,
+    })
+
+    const cookieStore = await cookies()
+    cookieStore.set('oauth_state', statePayload, {
+      httpOnly: true,
+      secure: process.env.NODE_ENV === 'production',
+      sameSite: 'lax',
+      maxAge: 600, // 10 minutes
+      path: '/',
+    })
+
+    const authUrl = buildGoogleAuthUrl(stateToken)
+    return NextResponse.redirect(authUrl)
+  } catch (err) {
+    console.error('Google authorize error:', err)
+    const message = err instanceof Error ? err.message : 'OAuth configuration error'
+
+    if (message.includes('not configured')) {
+      return NextResponse.json(
+        { error: 'Google Calendar integration is not yet configured' },
+        { status: 503 }
+      )
+    }
+
+    return NextResponse.json({ error: 'Failed to initiate OAuth' }, { status: 500 })
+  }
+}
diff --git a/src/app/api/auth/google/callback/route.ts b/src/app/api/auth/google/callback/route.ts
new file mode 100644
index 0000000..920bbdb
--- /dev/null
+++ b/src/app/api/auth/google/callback/route.ts
@@ -0,0 +1,89 @@
+import { NextRequest, NextResponse } from 'next/server'
+import { exchangeGoogleCode, fetchGoogleCalendars } from '@/lib/oauth'
+import { storePendingToken } from '@/lib/pending-tokens'
+import { cookies } from 'next/headers'
+
+/**
+ * GET /api/auth/google/callback
+ * Handles the OAuth callback from Google.
+ * Validates CSRF state, exchanges code for tokens, stores tokens in memory
+ * for one-time client retrieval, then redirects to calendar page.
+ */
+export async function GET(request: NextRequest) {
+  try {
+    const { searchParams } = new URL(request.url)
+    const code = searchParams.get('code')
+    const state = searchParams.get('state')
+    const error = searchParams.get('error')
+
+    if (error) {
+      return NextResponse.redirect(new URL('/rcal/calendar?connect=denied', request.url))
+    }
+
+    if (!code || !state) {
+      return NextResponse.redirect(
+        new URL('/rcal/calendar?connect=error&reason=missing_params', request.url)
+      )
+    }
+
+    // Validate CSRF state token
+    const cookieStore = await cookies()
+    const stateCookie = cookieStore.get('oauth_state')
+    if (!stateCookie?.value) {
+      return NextResponse.redirect(
+        new URL('/rcal/calendar?connect=error&reason=expired_session', request.url)
+      )
+    }
+
+    let statePayload: { csrf: string; userId: string }
+    try {
+      statePayload = JSON.parse(stateCookie.value)
+    } catch {
+      return NextResponse.redirect(
+        new URL('/rcal/calendar?connect=error&reason=invalid_state', request.url)
+      )
+    }
+
+    if (statePayload.csrf !== state) {
+      return NextResponse.redirect(
+        new URL('/rcal/calendar?connect=error&reason=csrf_mismatch', request.url)
+      )
+    }
+
+    // Clear the state cookie
+    cookieStore.delete('oauth_state')
+
+    // Exchange authorization code for tokens (server-side, uses client_secret)
+    const tokens = await exchangeGoogleCode(code)
+
+    // Fetch the user's calendars to find the primary one
+    const calendars = await fetchGoogleCalendars(tokens.access_token)
+
+    // Generate a one-time retrieval code (NOT the OAuth tokens themselves)
+    const retrievalCode = crypto.randomUUID()
+
+    // Store tokens in memory for one-time pickup (60 second TTL)
+    storePendingToken(retrievalCode, {
+      provider: 'google',
+      access_token: tokens.access_token,
+      refresh_token: tokens.refresh_token,
+      expires_in: tokens.expires_in,
+      calendars: calendars.map((c) => ({
+        id: c.id,
+        name: c.summary,
+        color: c.backgroundColor,
+        primary: c.primary,
+      })),
+    })
+
+    // Redirect to client with only the retrieval code — no tokens in the URL
+    return NextResponse.redirect(
+      new URL(`/rcal/calendar?connect=pending&rc=${retrievalCode}`, request.url)
+    )
+  } catch (err) {
+    console.error('Google callback error:', err)
+    return NextResponse.redirect(
+      new URL('/rcal/calendar?connect=error&reason=exchange_failed', request.url)
+    )
+  }
+}
diff --git a/src/app/api/auth/google/refresh/route.ts b/src/app/api/auth/google/refresh/route.ts
new file mode 100644
index 0000000..f111ba7
--- /dev/null
+++ b/src/app/api/auth/google/refresh/route.ts
@@ -0,0 +1,32 @@
+import { NextRequest, NextResponse } from 'next/server'
+import { requireAuth, isAuthed } from '@/lib/auth'
+import { refreshGoogleToken } from '@/lib/oauth'
+
+/**
+ * POST /api/auth/google/refresh
+ * Refreshes a Google access token using the refresh token.
+ * The client decrypts its stored refresh token and sends it here.
+ * Server uses the client_secret (from Infisical) to perform the refresh,
+ * returns the new access token. Neither token is persisted server-side.
+ */
+export async function POST(request: NextRequest) {
+  try {
+    const auth = await requireAuth(request)
+    if (!isAuthed(auth)) return auth
+
+    const { refresh_token } = await request.json()
+    if (!refresh_token || typeof refresh_token !== 'string') {
+      return NextResponse.json({ error: 'Missing refresh_token' }, { status: 400 })
+    }
+
+    const result = await refreshGoogleToken(refresh_token)
+
+    return NextResponse.json({
+      access_token: result.access_token,
+      expires_in: result.expires_in,
+    })
+  } catch (err) {
+    console.error('Token refresh error:', err)
+    return NextResponse.json({ error: 'Failed to refresh token' }, { status: 500 })
+  }
+}
diff --git a/src/app/api/auth/google/retrieve/route.ts b/src/app/api/auth/google/retrieve/route.ts
new file mode 100644
index 0000000..31bc81c
--- /dev/null
+++ b/src/app/api/auth/google/retrieve/route.ts
@@ -0,0 +1,36 @@
+import { NextRequest, NextResponse } from 'next/server'
+import { requireAuth, isAuthed } from '@/lib/auth'
+import { getPendingToken } from '@/lib/pending-tokens'
+
+/**
+ * POST /api/auth/google/retrieve
+ * One-time retrieval of OAuth tokens after successful callback.
+ * Requires authentication. Returns tokens exactly once; they are deleted
+ * from server memory after retrieval. The client must encrypt them with
+ * EncryptID before storing.
+ */
+export async function POST(request: NextRequest) {
+  try {
+    const auth = await requireAuth(request)
+    if (!isAuthed(auth)) return auth
+
+    const { code } = await request.json()
+    if (!code || typeof code !== 'string') {
+      return NextResponse.json({ error: 'Missing retrieval code' }, { status: 400 })
+    }
+
+    const tokenData = getPendingToken(code)
+    if (!tokenData) {
+      return NextResponse.json(
+        { error: 'Token expired or already retrieved' },
+        { status: 410 }
+      )
+    }
+
+    // Return tokens — client will encrypt with EncryptID immediately
+    return NextResponse.json(tokenData)
+  } catch (err) {
+    console.error('Token retrieval error:', err)
+    return NextResponse.json({ error: 'Failed to retrieve tokens' }, { status: 500 })
+  }
+}
diff --git a/src/app/api/auth/microsoft/authorize/route.ts b/src/app/api/auth/microsoft/authorize/route.ts
new file mode 100644
index 0000000..ae3b799
--- /dev/null
+++ b/src/app/api/auth/microsoft/authorize/route.ts
@@ -0,0 +1,46 @@
+import { NextRequest, NextResponse } from 'next/server'
+import { requireAuth, isAuthed } from '@/lib/auth'
+import { buildMicrosoftAuthUrl, generateStateToken } from '@/lib/oauth'
+import { cookies } from 'next/headers'
+
+/**
+ * GET /api/auth/microsoft/authorize
+ * Generates a Microsoft OAuth URL and redirects the user.
+ */
+export async function GET(request: NextRequest) {
+  try {
+    const auth = await requireAuth(request)
+    if (!isAuthed(auth)) return auth
+
+    const stateToken = generateStateToken()
+
+    const statePayload = JSON.stringify({
+      csrf: stateToken,
+      userId: auth.user.id,
+    })
+
+    const cookieStore = await cookies()
+    cookieStore.set('oauth_state', statePayload, {
+      httpOnly: true,
+      secure: process.env.NODE_ENV === 'production',
+      sameSite: 'lax',
+      maxAge: 600,
+      path: '/',
+    })
+
+    const authUrl = buildMicrosoftAuthUrl(stateToken)
+    return NextResponse.redirect(authUrl)
+  } catch (err) {
+    console.error('Microsoft authorize error:', err)
+    const message = err instanceof Error ? err.message : 'OAuth configuration error'
+
+    if (message.includes('not configured')) {
+      return NextResponse.json(
+        { error: 'Microsoft Calendar integration is not yet configured' },
+        { status: 503 }
+      )
+    }
+
+    return NextResponse.json({ error: 'Failed to initiate OAuth' }, { status: 500 })
+  }
+}
diff --git a/src/app/api/auth/microsoft/callback/route.ts b/src/app/api/auth/microsoft/callback/route.ts
new file mode 100644
index 0000000..031e609
--- /dev/null
+++ b/src/app/api/auth/microsoft/callback/route.ts
@@ -0,0 +1,74 @@
+import { NextRequest, NextResponse } from 'next/server'
+import { exchangeMicrosoftCode } from '@/lib/oauth'
+import { storePendingToken } from '@/lib/pending-tokens'
+import { cookies } from 'next/headers'
+
+/**
+ * GET /api/auth/microsoft/callback
+ * Handles the OAuth callback from Microsoft.
+ * Tokens stored in memory for one-time client retrieval + EncryptID encryption.
+ */
+export async function GET(request: NextRequest) {
+  try {
+    const { searchParams } = new URL(request.url)
+    const code = searchParams.get('code')
+    const state = searchParams.get('state')
+    const error = searchParams.get('error')
+
+    if (error) {
+      return NextResponse.redirect(new URL('/rcal/calendar?connect=denied', request.url))
+    }
+
+    if (!code || !state) {
+      return NextResponse.redirect(
+        new URL('/rcal/calendar?connect=error&reason=missing_params', request.url)
+      )
+    }
+
+    const cookieStore = await cookies()
+    const stateCookie = cookieStore.get('oauth_state')
+    if (!stateCookie?.value) {
+      return NextResponse.redirect(
+        new URL('/rcal/calendar?connect=error&reason=expired_session', request.url)
+      )
+    }
+
+    let statePayload: { csrf: string; userId: string }
+    try {
+      statePayload = JSON.parse(stateCookie.value)
+    } catch {
+      return NextResponse.redirect(
+        new URL('/rcal/calendar?connect=error&reason=invalid_state', request.url)
+      )
+    }
+
+    if (statePayload.csrf !== state) {
+      return NextResponse.redirect(
+        new URL('/rcal/calendar?connect=error&reason=csrf_mismatch', request.url)
+      )
+    }
+
+    cookieStore.delete('oauth_state')
+
+    const tokens = await exchangeMicrosoftCode(code)
+
+    const retrievalCode = crypto.randomUUID()
+
+    storePendingToken(retrievalCode, {
+      provider: 'outlook',
+      access_token: tokens.access_token,
+      refresh_token: tokens.refresh_token,
+      expires_in: tokens.expires_in,
+      calendars: [{ id: 'primary', name: 'Outlook Calendar', color: '#0078d4', primary: true }],
+    })
+
+    return NextResponse.redirect(
+      new URL(`/rcal/calendar?connect=pending&rc=${retrievalCode}`, request.url)
+    )
+  } catch (err) {
+    console.error('Microsoft callback error:', err)
+    return NextResponse.redirect(
+      new URL('/rcal/calendar?connect=error&reason=exchange_failed', request.url)
+    )
+  }
+}
diff --git a/src/app/calendar/page.tsx b/src/app/calendar/page.tsx
index 183e225..7db3c4a 100644
--- a/src/app/calendar/page.tsx
+++ b/src/app/calendar/page.tsx
@@ -1,10 +1,11 @@
 'use client'
 
-import { useState, useEffect, useCallback } from 'react'
+import { useState, useEffect, useCallback, Suspense } from 'react'
 import { Calendar as CalendarIcon, MapPin, Clock, ZoomIn, ZoomOut, Link2, Unlink2 } from 'lucide-react'
 import { TemporalZoomController } from '@/components/calendar'
 import { CalendarHeader } from '@/components/calendar/CalendarHeader'
 import { CalendarSidebar } from '@/components/calendar/CalendarSidebar'
+import { ConnectCalendarBanner } from '@/components/ConnectCalendarBanner'
 import { TabLayout } from '@/components/ui/TabLayout'
 import { TemporalTab } from '@/components/tabs/TemporalTab'
 import { SpatialTab } from '@/components/tabs/SpatialTab'
@@ -76,6 +77,9 @@ export default function Home() {
 
       {/* Main content */}
       <div className="flex-1 flex flex-col overflow-hidden">
+        <Suspense fallback={null}>
+          <ConnectCalendarBanner />
+        </Suspense>
         <CalendarHeader
           onToggleSidebar={() => setSidebarOpen(!sidebarOpen)}
           sidebarOpen={sidebarOpen}
diff --git a/src/components/ConnectCalendarBanner.tsx b/src/components/ConnectCalendarBanner.tsx
new file mode 100644
index 0000000..abb1c13
--- /dev/null
+++ b/src/components/ConnectCalendarBanner.tsx
@@ -0,0 +1,268 @@
+'use client'
+
+import { useState, useEffect, useCallback } from 'react'
+import { Calendar, X, ChevronRight, AlertCircle, CheckCircle2, Shield } from 'lucide-react'
+import { useSearchParams } from 'next/navigation'
+import {
+  useCalendarTokens,
+  encryptAndStoreTokens,
+  getConnectedProviders,
+} from '@/hooks/useCalendarTokens'
+
+const DISMISS_KEY = 'rcal-connect-banner-dismissed'
+
+const PROVIDERS = [
+  {
+    id: 'google',
+    name: 'Google Calendar',
+    icon: (
+      <svg viewBox="0 0 24 24" className="w-5 h-5" fill="none">
+        <path d="M22.56 12.25c0-.78-.07-1.53-.2-2.25H12v4.26h5.92a5.06 5.06 0 01-2.2 3.32v2.77h3.57c2.08-1.92 3.28-4.74 3.28-8.1z" fill="#4285F4"/>
+        <path d="M12 23c2.97 0 5.46-.98 7.28-2.66l-3.57-2.77c-.98.66-2.23 1.06-3.71 1.06-2.86 0-5.29-1.93-6.16-4.53H2.18v2.84C3.99 20.53 7.7 23 12 23z" fill="#34A853"/>
+        <path d="M5.84 14.09c-.22-.66-.35-1.36-.35-2.09s.13-1.43.35-2.09V7.07H2.18C1.43 8.55 1 10.22 1 12s.43 3.45 1.18 4.93l2.85-2.22.81-.62z" fill="#FBBC05"/>
+        <path d="M12 5.38c1.62 0 3.06.56 4.21 1.64l3.15-3.15C17.45 2.09 14.97 1 12 1 7.7 1 3.99 3.47 2.18 7.07l3.66 2.84c.87-2.6 3.3-4.53 6.16-4.53z" fill="#EA4335"/>
+      </svg>
+    ),
+    href: '/rcal/api/auth/google/authorize',
+    color: 'hover:border-blue-400 hover:bg-blue-50 dark:hover:bg-blue-950/30',
+  },
+  {
+    id: 'outlook',
+    name: 'Outlook / Microsoft 365',
+    icon: (
+      <svg viewBox="0 0 24 24" className="w-5 h-5" fill="#0078D4">
+        <path d="M24 7.387v10.478c0 .23-.08.424-.238.576a.807.807 0 01-.588.234h-8.42v-6.56l1.56 1.14a.27.27 0 00.32 0l7.14-5.088c.08-.058.155-.058.226 0zM24 5.395c0-.07-.038-.15-.113-.234a.348.348 0 00-.238-.14h-.146L14.754 11.5l-1.504-1.09V4.5h10.4c.346 0 .566.1.7.297.1.197.15.398.15.598zM13.25 4.5v7.122L1.2 4.68c-.1-.06-.176-.03-.226.088A.756.756 0 00.9 5.1v14.287a.734.734 0 00.247.556c.165.15.354.227.566.227h11.537V12.68l-.34.244-.002.001-4.254 3.025a.27.27 0 01-.318 0L1.574 11.2v5.556a.368.368 0 01-.114.27.368.368 0 01-.272.114.379.379 0 01-.384-.384V8.92l6.762 4.808a.27.27 0 00.318 0L13.25 9.99V4.5z"/>
+      </svg>
+    ),
+    href: '/rcal/api/auth/microsoft/authorize',
+    color: 'hover:border-sky-400 hover:bg-sky-50 dark:hover:bg-sky-950/30',
+  },
+  {
+    id: 'ics',
+    name: 'ICS / iCal URL',
+    icon: <Calendar className="w-5 h-5 text-orange-500" />,
+    href: null,
+    color: 'hover:border-orange-400 hover:bg-orange-50 dark:hover:bg-orange-950/30',
+    isManual: true,
+  },
+] as Array<{
+  id: string
+  name: string
+  icon: React.ReactNode
+  href: string | null
+  color: string
+  isManual?: boolean
+}>
+
+export function ConnectCalendarBanner() {
+  const [dismissed, setDismissed] = useState(true)
+  const [loading, setLoading] = useState(true)
+  const [showProviders, setShowProviders] = useState(false)
+  const [connectStatus, setConnectStatus] = useState<
+    'idle' | 'success' | 'denied' | 'error' | 'encrypting'
+  >('idle')
+  const [isAuthenticated, setIsAuthenticated] = useState(false)
+  const searchParams = useSearchParams()
+  const { hasConnected, refresh: refreshProviders } = useCalendarTokens()
+
+  // Check auth status
+  useEffect(() => {
+    fetch('/api/me')
+      .then((r) => r.json())
+      .then((data) => {
+        setIsAuthenticated(!!data.authenticated)
+      })
+      .catch(() => {})
+      .finally(() => setLoading(false))
+  }, [])
+
+  // Handle OAuth callback — retrieve tokens and encrypt with EncryptID
+  useEffect(() => {
+    const connect = searchParams.get('connect')
+    const retrievalCode = searchParams.get('rc')
+
+    if (connect === 'pending' && retrievalCode) {
+      setConnectStatus('encrypting')
+      // Retrieve tokens from server and encrypt locally
+      ;(async () => {
+        try {
+          const response = await fetch('/api/auth/google/retrieve', {
+            method: 'POST',
+            headers: { 'Content-Type': 'application/json' },
+            body: JSON.stringify({ code: retrievalCode }),
+          })
+
+          if (!response.ok) {
+            throw new Error(`Retrieval failed: ${response.status}`)
+          }
+
+          const tokenData = await response.json()
+
+          // Encrypt with EncryptID and store in localStorage
+          await encryptAndStoreTokens(tokenData.provider, tokenData)
+
+          setConnectStatus('success')
+          refreshProviders()
+          window.history.replaceState({}, '', '/rcal/calendar')
+
+          setTimeout(() => setConnectStatus('idle'), 5000)
+        } catch (err) {
+          console.error('Token encryption failed:', err)
+          setConnectStatus('error')
+          window.history.replaceState({}, '', '/rcal/calendar')
+          setTimeout(() => setConnectStatus('idle'), 5000)
+        }
+      })()
+    } else if (connect === 'denied') {
+      setConnectStatus('denied')
+      window.history.replaceState({}, '', '/rcal/calendar')
+      setTimeout(() => setConnectStatus('idle'), 5000)
+    } else if (connect === 'error') {
+      setConnectStatus('error')
+      window.history.replaceState({}, '', '/rcal/calendar')
+      setTimeout(() => setConnectStatus('idle'), 5000)
+    }
+  }, [searchParams, refreshProviders])
+
+  // Determine banner visibility
+  useEffect(() => {
+    if (!loading && isAuthenticated) {
+      const wasDismissed = localStorage.getItem(DISMISS_KEY)
+      const connected = getConnectedProviders().length > 0
+      setDismissed(connected || !!wasDismissed)
+    }
+  }, [loading, isAuthenticated, hasConnected])
+
+  const handleDismiss = useCallback(() => {
+    setDismissed(true)
+    localStorage.setItem(DISMISS_KEY, 'true')
+  }, [])
+
+  // Success toast
+  if (connectStatus === 'success') {
+    return (
+      <div className="bg-green-50 dark:bg-green-950/40 border-b border-green-200 dark:border-green-800 px-4 py-3">
+        <div className="flex items-center gap-3 max-w-screen-xl mx-auto">
+          <CheckCircle2 className="w-5 h-5 text-green-600 dark:text-green-400 flex-shrink-0" />
+          <p className="text-sm text-green-800 dark:text-green-200 flex-1">
+            Calendar connected! Credentials encrypted with your passkey and stored locally.
+          </p>
+          <button
+            onClick={() => setConnectStatus('idle')}
+            className="p-1 rounded hover:bg-green-100 dark:hover:bg-green-900 transition-colors"
+          >
+            <X className="w-4 h-4 text-green-600 dark:text-green-400" />
+          </button>
+        </div>
+      </div>
+    )
+  }
+
+  // Encrypting state
+  if (connectStatus === 'encrypting') {
+    return (
+      <div className="bg-blue-50 dark:bg-blue-950/40 border-b border-blue-200 dark:border-blue-800 px-4 py-3">
+        <div className="flex items-center gap-3 max-w-screen-xl mx-auto">
+          <Shield className="w-5 h-5 text-blue-600 dark:text-blue-400 flex-shrink-0 animate-pulse" />
+          <p className="text-sm text-blue-800 dark:text-blue-200 flex-1">
+            Encrypting your calendar credentials with your passkey...
+          </p>
+        </div>
+      </div>
+    )
+  }
+
+  // Error/denied toast
+  if (connectStatus === 'error' || connectStatus === 'denied') {
+    return (
+      <div className="bg-red-50 dark:bg-red-950/40 border-b border-red-200 dark:border-red-800 px-4 py-3">
+        <div className="flex items-center gap-3 max-w-screen-xl mx-auto">
+          <AlertCircle className="w-5 h-5 text-red-600 dark:text-red-400 flex-shrink-0" />
+          <p className="text-sm text-red-800 dark:text-red-200 flex-1">
+            {connectStatus === 'denied'
+              ? 'Calendar access was denied. You can try again anytime.'
+              : 'Failed to connect calendar. Please try again.'}
+          </p>
+          <button
+            onClick={() => setConnectStatus('idle')}
+            className="p-1 rounded hover:bg-red-100 dark:hover:bg-red-900 transition-colors"
+          >
+            <X className="w-4 h-4 text-red-600 dark:text-red-400" />
+          </button>
+        </div>
+      </div>
+    )
+  }
+
+  // Don't render while loading, if not authenticated, or if dismissed
+  if (loading || !isAuthenticated || dismissed) return null
+
+  return (
+    <div className="bg-blue-50 dark:bg-blue-950/40 border-b border-blue-200 dark:border-blue-800">
+      <div className="px-4 py-3 max-w-screen-xl mx-auto">
+        <div className="flex items-center gap-3">
+          <div className="flex-shrink-0 w-8 h-8 rounded-full bg-blue-100 dark:bg-blue-900/60 flex items-center justify-center">
+            <Calendar className="w-4 h-4 text-blue-600 dark:text-blue-400" />
+          </div>
+
+          <div className="flex-1 min-w-0">
+            <p className="text-sm font-medium text-blue-900 dark:text-blue-100">
+              Connect your calendar
+            </p>
+            <p className="text-xs text-blue-700 dark:text-blue-300 mt-0.5">
+              Sync events from Google Calendar, Outlook, or import via ICS. Credentials are encrypted locally with your passkey.
+            </p>
+          </div>
+
+          <div className="flex items-center gap-2 flex-shrink-0">
+            <button
+              onClick={() => setShowProviders(!showProviders)}
+              className="inline-flex items-center gap-1.5 px-3 py-1.5 text-sm font-medium text-white bg-blue-600 hover:bg-blue-700 dark:bg-blue-500 dark:hover:bg-blue-600 rounded-lg transition-colors"
+            >
+              Connect
+              <ChevronRight className={`w-3.5 h-3.5 transition-transform ${showProviders ? 'rotate-90' : ''}`} />
+            </button>
+            <button
+              onClick={handleDismiss}
+              className="p-1 rounded hover:bg-blue-100 dark:hover:bg-blue-900 transition-colors"
+              title="Dismiss"
+            >
+              <X className="w-4 h-4 text-blue-400 dark:text-blue-500" />
+            </button>
+          </div>
+        </div>
+
+        {showProviders && (
+          <div className="mt-3 pt-3 border-t border-blue-200 dark:border-blue-800">
+            <div className="grid grid-cols-1 sm:grid-cols-3 gap-2">
+              {PROVIDERS.map((provider) => (
+                <a
+                  key={provider.id}
+                  href={provider.href || undefined}
+                  onClick={
+                    provider.isManual
+                      ? (e) => {
+                          e.preventDefault()
+                          alert('ICS import coming soon — use the sidebar "Add calendar" button for now.')
+                        }
+                      : undefined
+                  }
+                  className={`flex items-center gap-3 px-3 py-2.5 rounded-lg border border-gray-200 dark:border-gray-700 bg-white dark:bg-gray-800 transition-colors cursor-pointer ${provider.color}`}
+                >
+                  {provider.icon}
+                  <span className="text-sm font-medium text-gray-900 dark:text-gray-100">
+                    {provider.name}
+                  </span>
+                </a>
+              ))}
+            </div>
+            <div className="mt-2 flex items-center gap-1.5 text-xs text-blue-600 dark:text-blue-400">
+              <Shield className="w-3.5 h-3.5" />
+              Read-only access. Tokens are encrypted with your passkey (AES-256-GCM) and stored only in your browser.
+            </div>
+          </div>
+        )}
+      </div>
+    </div>
+  )
+}
diff --git a/src/hooks/useCalendarTokens.ts b/src/hooks/useCalendarTokens.ts
new file mode 100644
index 0000000..26dddd9
--- /dev/null
+++ b/src/hooks/useCalendarTokens.ts
@@ -0,0 +1,211 @@
+'use client'
+
+/**
+ * useCalendarTokens — Manages OAuth tokens encrypted with EncryptID.
+ *
+ * Tokens are encrypted client-side using the user's passkey-derived AES-256-GCM
+ * key and stored in localStorage. The server never persists tokens.
+ *
+ * Storage format per provider in localStorage:
+ *   rcal_oauth_{provider} = JSON { ciphertext: base64, iv: base64 }
+ *
+ * Decrypted payload:
+ *   { access_token, refresh_token, expires_at, calendars }
+ */
+
+import { useState, useCallback } from 'react'
+import {
+  getKeyManager,
+  encryptData,
+  decryptDataAsString,
+  bufferToBase64url,
+  base64urlToBuffer,
+} from '@encryptid/sdk/client'
+
+const STORAGE_PREFIX = 'rcal_oauth_'
+
+export interface StoredCalendarTokens {
+  provider: string
+  access_token: string
+  refresh_token?: string
+  expires_at: number // Unix ms
+  calendars: Array<{
+    id: string
+    name: string
+    color?: string
+    primary?: boolean
+  }>
+}
+
+interface EncryptedBlob {
+  ciphertext: string // base64url
+  iv: string // base64url
+}
+
+/**
+ * Encrypt OAuth tokens with the user's EncryptID key and store in localStorage.
+ */
+export async function encryptAndStoreTokens(
+  provider: string,
+  tokens: {
+    access_token: string
+    refresh_token?: string
+    expires_in: number
+    calendars: Array<{ id: string; name: string; color?: string; primary?: boolean }>
+  }
+): Promise<void> {
+  const km = getKeyManager()
+  if (!km.isInitialized()) {
+    throw new Error('EncryptID key manager not initialized — please sign in with your passkey')
+  }
+
+  const keys = await km.getKeys()
+
+  const payload: StoredCalendarTokens = {
+    provider,
+    access_token: tokens.access_token,
+    refresh_token: tokens.refresh_token,
+    expires_at: Date.now() + tokens.expires_in * 1000,
+    calendars: tokens.calendars,
+  }
+
+  const encrypted = await encryptData(keys.encryptionKey, JSON.stringify(payload))
+
+  const blob: EncryptedBlob = {
+    ciphertext: bufferToBase64url(encrypted.ciphertext),
+    iv: bufferToBase64url(encrypted.iv.buffer as ArrayBuffer),
+  }
+
+  localStorage.setItem(`${STORAGE_PREFIX}${provider}`, JSON.stringify(blob))
+}
+
+/**
+ * Decrypt stored tokens for a provider.
+ */
+export async function decryptStoredTokens(provider: string): Promise<StoredCalendarTokens | null> {
+  const stored = localStorage.getItem(`${STORAGE_PREFIX}${provider}`)
+  if (!stored) return null
+
+  const km = getKeyManager()
+  if (!km.isInitialized()) return null
+
+  try {
+    const keys = await km.getKeys()
+    const blob: EncryptedBlob = JSON.parse(stored)
+
+    const decrypted = await decryptDataAsString(keys.encryptionKey, {
+      ciphertext: base64urlToBuffer(blob.ciphertext),
+      iv: new Uint8Array(base64urlToBuffer(blob.iv)),
+    })
+
+    return JSON.parse(decrypted) as StoredCalendarTokens
+  } catch (err) {
+    console.error(`Failed to decrypt ${provider} tokens:`, err)
+    return null
+  }
+}
+
+/**
+ * Remove stored tokens for a provider.
+ */
+export function removeStoredTokens(provider: string): void {
+  localStorage.removeItem(`${STORAGE_PREFIX}${provider}`)
+}
+
+/**
+ * Check which providers have stored (encrypted) tokens.
+ */
+export function getConnectedProviders(): string[] {
+  const providers: string[] = []
+  for (let i = 0; i < localStorage.length; i++) {
+    const key = localStorage.key(i)
+    if (key?.startsWith(STORAGE_PREFIX)) {
+      providers.push(key.slice(STORAGE_PREFIX.length))
+    }
+  }
+  return providers
+}
+
+/**
+ * Refresh an expired access token via the server.
+ * Decrypts refresh_token, sends to server, gets new access_token,
+ * re-encrypts and stores the updated tokens.
+ */
+export async function refreshAndUpdateTokens(provider: string): Promise<StoredCalendarTokens | null> {
+  const tokens = await decryptStoredTokens(provider)
+  if (!tokens?.refresh_token) return null
+
+  try {
+    const response = await fetch(`/api/auth/${provider}/refresh`, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ refresh_token: tokens.refresh_token }),
+    })
+
+    if (!response.ok) {
+      if (response.status === 401) {
+        // Refresh token revoked — remove stored tokens
+        removeStoredTokens(provider)
+        return null
+      }
+      throw new Error(`Refresh failed: ${response.status}`)
+    }
+
+    const result = await response.json()
+
+    // Re-encrypt with updated access token
+    await encryptAndStoreTokens(provider, {
+      access_token: result.access_token,
+      refresh_token: tokens.refresh_token, // Keep existing refresh token
+      expires_in: result.expires_in,
+      calendars: tokens.calendars,
+    })
+
+    return await decryptStoredTokens(provider)
+  } catch (err) {
+    console.error(`Failed to refresh ${provider} token:`, err)
+    return null
+  }
+}
+
+/**
+ * Get a valid access token, refreshing if expired.
+ */
+export async function getValidAccessToken(provider: string): Promise<string | null> {
+  let tokens = await decryptStoredTokens(provider)
+  if (!tokens) return null
+
+  // If token expires within 2 minutes, refresh
+  if (tokens.expires_at < Date.now() + 120_000) {
+    tokens = await refreshAndUpdateTokens(provider)
+    if (!tokens) return null
+  }
+
+  return tokens.access_token
+}
+
+/**
+ * React hook for calendar token state.
+ */
+export function useCalendarTokens() {
+  const [connectedProviders, setConnectedProviders] = useState<string[]>(() => {
+    if (typeof window === 'undefined') return []
+    return getConnectedProviders()
+  })
+
+  const refresh = useCallback(() => {
+    setConnectedProviders(getConnectedProviders())
+  }, [])
+
+  const disconnect = useCallback((provider: string) => {
+    removeStoredTokens(provider)
+    setConnectedProviders(getConnectedProviders())
+  }, [])
+
+  return {
+    connectedProviders,
+    hasConnected: connectedProviders.length > 0,
+    refresh,
+    disconnect,
+  }
+}
diff --git a/src/lib/oauth.ts b/src/lib/oauth.ts
new file mode 100644
index 0000000..c755450
--- /dev/null
+++ b/src/lib/oauth.ts
@@ -0,0 +1,245 @@
+/**
+ * OAuth 2.0 helpers for calendar provider integrations.
+ * Server-side only — handles code exchange with provider secrets from Infisical.
+ * Tokens are returned to the client for EncryptID encryption; never persisted server-side.
+ */
+
+// ── Google Calendar OAuth ──
+
+const GOOGLE_AUTH_URL = 'https://accounts.google.com/o/oauth2/v2/auth'
+const GOOGLE_TOKEN_URL = 'https://oauth2.googleapis.com/token'
+
+const GOOGLE_SCOPES = [
+  'https://www.googleapis.com/auth/calendar.readonly',
+  'https://www.googleapis.com/auth/calendar.events.readonly',
+].join(' ')
+
+function getGoogleCredentials() {
+  const clientId = process.env.GOOGLE_CLIENT_ID
+  const clientSecret = process.env.GOOGLE_CLIENT_SECRET
+  const redirectUri = process.env.GOOGLE_OAUTH_REDIRECT_URI ||
+    `${process.env.NEXT_PUBLIC_APP_URL || 'https://rspace.online/rcal'}/api/auth/google/callback`
+
+  if (!clientId || !clientSecret) {
+    throw new Error('Google OAuth credentials not configured')
+  }
+
+  return { clientId, clientSecret, redirectUri }
+}
+
+/**
+ * Generate a Google OAuth 2.0 authorization URL.
+ * Includes a CSRF state token that must be verified on callback.
+ */
+export function buildGoogleAuthUrl(stateToken: string): string {
+  const { clientId, redirectUri } = getGoogleCredentials()
+
+  const params = new URLSearchParams({
+    client_id: clientId,
+    redirect_uri: redirectUri,
+    response_type: 'code',
+    scope: GOOGLE_SCOPES,
+    access_type: 'offline',
+    prompt: 'consent',
+    state: stateToken,
+  })
+
+  return `${GOOGLE_AUTH_URL}?${params.toString()}`
+}
+
+/**
+ * Exchange an authorization code for tokens. Server-side only.
+ * Returns tokens that the client will encrypt with EncryptID.
+ */
+export async function exchangeGoogleCode(code: string): Promise<{
+  access_token: string
+  refresh_token?: string
+  expires_in: number
+  token_type: string
+  scope: string
+}> {
+  const { clientId, clientSecret, redirectUri } = getGoogleCredentials()
+
+  const response = await fetch(GOOGLE_TOKEN_URL, {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
+    body: new URLSearchParams({
+      code,
+      client_id: clientId,
+      client_secret: clientSecret,
+      redirect_uri: redirectUri,
+      grant_type: 'authorization_code',
+    }),
+  })
+
+  if (!response.ok) {
+    const error = await response.text()
+    throw new Error(`Google token exchange failed: ${error}`)
+  }
+
+  return response.json()
+}
+
+/**
+ * Refresh an access token using a refresh token. Server-side only.
+ * Called when the client sends an expired token for sync.
+ */
+export async function refreshGoogleToken(refreshToken: string): Promise<{
+  access_token: string
+  expires_in: number
+  token_type: string
+  scope: string
+}> {
+  const { clientId, clientSecret } = getGoogleCredentials()
+
+  const response = await fetch(GOOGLE_TOKEN_URL, {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
+    body: new URLSearchParams({
+      refresh_token: refreshToken,
+      client_id: clientId,
+      client_secret: clientSecret,
+      grant_type: 'refresh_token',
+    }),
+  })
+
+  if (!response.ok) {
+    const error = await response.text()
+    throw new Error(`Google token refresh failed: ${error}`)
+  }
+
+  return response.json()
+}
+
+/**
+ * Fetch events from Google Calendar using a user-provided access token.
+ * Token is ephemeral — passed per-request, never stored.
+ */
+export async function fetchGoogleCalendarEvents(
+  accessToken: string,
+  calendarId: string = 'primary',
+  timeMin?: string,
+  timeMax?: string,
+): Promise<Array<Record<string, unknown>>> {
+  const params = new URLSearchParams({
+    singleEvents: 'true',
+    orderBy: 'startTime',
+    maxResults: '2500',
+  })
+  if (timeMin) params.set('timeMin', timeMin)
+  if (timeMax) params.set('timeMax', timeMax)
+
+  const response = await fetch(
+    `https://www.googleapis.com/calendar/v3/calendars/${encodeURIComponent(calendarId)}/events?${params}`,
+    { headers: { Authorization: `Bearer ${accessToken}` } }
+  )
+
+  if (!response.ok) {
+    throw new Error(`Google Calendar API error: ${response.status}`)
+  }
+
+  const data = await response.json()
+  return data.items || []
+}
+
+/**
+ * Fetch user's Google calendar list to let them choose which to sync.
+ */
+export async function fetchGoogleCalendars(accessToken: string): Promise<Array<{
+  id: string
+  summary: string
+  description?: string
+  backgroundColor?: string
+  primary?: boolean
+}>> {
+  const response = await fetch(
+    'https://www.googleapis.com/calendar/v3/users/me/calendarList',
+    { headers: { Authorization: `Bearer ${accessToken}` } }
+  )
+
+  if (!response.ok) {
+    throw new Error(`Failed to fetch Google calendars: ${response.status}`)
+  }
+
+  const data = await response.json()
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  return (data.items || []).map((cal: any) => ({
+    id: cal.id as string,
+    summary: cal.summary as string,
+    description: cal.description as string | undefined,
+    backgroundColor: cal.backgroundColor as string | undefined,
+    primary: cal.primary as boolean | undefined,
+  }))
+}
+
+// ── Outlook/Microsoft Calendar OAuth ──
+
+const MS_AUTH_URL = 'https://login.microsoftonline.com/common/oauth2/v2.0/authorize'
+const MS_TOKEN_URL = 'https://login.microsoftonline.com/common/oauth2/v2.0/token'
+
+const MS_SCOPES = ['Calendars.Read', 'offline_access'].join(' ')
+
+function getMicrosoftCredentials() {
+  const clientId = process.env.MICROSOFT_OAUTH_CLIENT_ID
+  const clientSecret = process.env.MICROSOFT_OAUTH_CLIENT_SECRET
+  const redirectUri = process.env.MICROSOFT_OAUTH_REDIRECT_URI ||
+    `${process.env.NEXT_PUBLIC_APP_URL || 'https://rspace.online/rcal'}/api/auth/microsoft/callback`
+
+  if (!clientId || !clientSecret) {
+    throw new Error('Microsoft OAuth credentials not configured')
+  }
+
+  return { clientId, clientSecret, redirectUri }
+}
+
+export function buildMicrosoftAuthUrl(stateToken: string): string {
+  const { clientId, redirectUri } = getMicrosoftCredentials()
+
+  const params = new URLSearchParams({
+    client_id: clientId,
+    redirect_uri: redirectUri,
+    response_type: 'code',
+    scope: MS_SCOPES,
+    state: stateToken,
+    response_mode: 'query',
+  })
+
+  return `${MS_AUTH_URL}?${params.toString()}`
+}
+
+export async function exchangeMicrosoftCode(code: string): Promise<{
+  access_token: string
+  refresh_token?: string
+  expires_in: number
+  token_type: string
+  scope: string
+}> {
+  const { clientId, clientSecret, redirectUri } = getMicrosoftCredentials()
+
+  const response = await fetch(MS_TOKEN_URL, {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
+    body: new URLSearchParams({
+      code,
+      client_id: clientId,
+      client_secret: clientSecret,
+      redirect_uri: redirectUri,
+      grant_type: 'authorization_code',
+    }),
+  })
+
+  if (!response.ok) {
+    const error = await response.text()
+    throw new Error(`Microsoft token exchange failed: ${error}`)
+  }
+
+  return response.json()
+}
+
+// ── Utility: generate CSRF state token ──
+
+export function generateStateToken(): string {
+  const array = new Uint8Array(32)
+  crypto.getRandomValues(array)
+  return Array.from(array, (b) => b.toString(16).padStart(2, '0')).join('')
+}
diff --git a/src/lib/pending-tokens.ts b/src/lib/pending-tokens.ts
new file mode 100644
index 0000000..7df9d97
--- /dev/null
+++ b/src/lib/pending-tokens.ts
@@ -0,0 +1,39 @@
+/**
+ * Temporary in-memory store for OAuth tokens pending client retrieval.
+ * Tokens live here for max 60 seconds before being picked up by the client,
+ * encrypted with EncryptID, and stored in the browser.
+ * NOT persisted — lives only in this server process's memory.
+ */
+
+const pendingTokens = new Map<string, { data: unknown; expiresAt: number }>()
+
+// Cleanup expired entries periodically
+if (typeof setInterval !== 'undefined') {
+  setInterval(() => {
+    const now = Date.now()
+    pendingTokens.forEach((entry, key) => {
+      if (now > entry.expiresAt) pendingTokens.delete(key)
+    })
+  }, 10_000)
+}
+
+export function storePendingToken(code: string, data: unknown, ttlMs = 60_000): void {
+  pendingTokens.set(code, {
+    data,
+    expiresAt: Date.now() + ttlMs,
+  })
+}
+
+/**
+ * One-time retrieval — deletes the token after reading.
+ */
+export function getPendingToken(code: string): unknown | null {
+  const entry = pendingTokens.get(code)
+  if (!entry) return null
+  if (Date.now() > entry.expiresAt) {
+    pendingTokens.delete(code)
+    return null
+  }
+  pendingTokens.delete(code)
+  return entry.data
+}