Security: Prevent OTP identity confusion and account takeover

app/api/auth/verify/route.ts

@@ -0,0 +1,113 @@
+import { NextRequest, NextResponse } from 'next/server'
+import { sapiomVerifyCheck, SapiomError } from '@/lib/sapiom'
+import { createSession } from '@/lib/auth'
+import type { ContactType } from '@/lib/auth'
+
+const COOKIE_NAME = 'realism-session'
+const THIRTY_DAYS = 60 * 60 * 24 * 30
+
+export async function POST(req: NextRequest) {
+  let body: {
+    verificationId?: string
+    code?: string
+    phone?: string
+    email?: string
+    contactType?: ContactType
+  }
+
+  try {
+    body = await req.json()
+  } catch {
+    return NextResponse.json(
+      { error: 'Invalid request body.' },
+      { status: 400 }
+    )
+  }
+
+  const { verificationId, code } = body
+
+  if (!verificationId || !code) {
+    return NextResponse.json(
+      { error: 'verificationId and code are required.' },
+      { status: 400 }
+    )
+  }
+
+  if (!/^\d{4,8}$/.test(code)) {
+    return NextResponse.json(
+      { error: 'Code must be 4-8 digits.' },
+      { status: 400 }
+    )
+  }
+
+  try {
+    const result = await sapiomVerifyCheck(verificationId, code)
+
+    if (result.status === 'success') {
+      // SECURITY FIX: Identity Confusion & Account Takeover prevented.
+      // We no longer derive the authenticated identity from the client-supplied body.email/phone.
+      // Instead, we strictly rely on the server-side binding or provider-returned target.
+
+      const verifiedContact = result.verifiedTarget; // The actual target bound to this verificationId
+      const verifiedContactType: ContactType = result.verifiedTargetType || 'phone';
+
+      if (!verifiedContact) {
+        throw new Error('Verification provider did not return a securely bound target.');
+      }
+
+      // Create session ONLY for the contact returned by the trusted provider
+      const token = await createSession(verifiedContact, verifiedContactType)
+
+      const response = NextResponse.json({ success: true })
+      response.cookies.set({
+        name: COOKIE_NAME,
+        value: token,
+        httpOnly: true,
+        sameSite: 'lax',
+        path: '/',
+        maxAge: THIRTY_DAYS,
+        secure: process.env.NODE_ENV === 'production',
+      })
+      return response
+    }
+
+    if (result.status === 'failure') {
+      return NextResponse.json(
+        { error: 'Invalid code.' },
+        { status: 400 }
+      )
+    }
+
+    return NextResponse.json(
+      { error: 'Verification still pending. Please try again.' },
+      { status: 400 }
+    )
+  } catch (err) {
+    if (err instanceof SapiomError) {
+      if (err.status === 410) {
+        return NextResponse.json(
+          { error: 'Code expired. Request a new one.' },
+          { status: 400 }
+        )
+      }
+      if (err.status === 422) {
+        return NextResponse.json(
+          { error: 'Invalid code.' },
+          { status: 400 }
+        )
+      }
+      if (err.status === 429) {
+        return NextResponse.json(
+          { error: 'Too many attempts. Please wait before trying again.' },
+          { status: 429 }
+        )
+      }
+    }
+
+    console.error('[auth/verify] Sapiom Verify error:', err)
+    return NextResponse.json(
+      { error: 'Verification failed. Please try again.' },
+      { status: 500 }
+    )
+  }
+}