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* CSRF Protection Module
*
* Provides Cross-Site Request Forgery (CSRF) protection for state-changing operations.
* Uses the Double Submit Cookie pattern combined with token validation.
*
* Security features:
* - Cryptographically secure token generation
* - Time-limited tokens with configurable expiry
* - Origin validation
* - SameSite cookie enforcement
*/
import { createHash, randomBytes } from "crypto";
import { cookies } from "next/headers";
import { NextRequest, NextResponse } from "next/server";
import { TOKEN_CONFIG } from '@/lib/security';
const CSRF_COOKIE_NAME = "__csrf_token";
const CSRF_HEADER_NAME = "x-csrf-token";
interface CsrfTokenData {
token: string;
timestamp: number;
}
/**
* Generate a cryptographically secure CSRF token
*/
export function generateCsrfToken(): string {
const token = randomBytes(TOKEN_CONFIG.TOKEN_BYTES).toString("hex");
const timestamp = Date.now();
const data: CsrfTokenData = { token, timestamp };
return Buffer.from(JSON.stringify(data)).toString("base64");
}
/**
* Parse a CSRF token to extract its data
*/
function parseCsrfToken(encodedToken: string): CsrfTokenData | null {
try {
const decoded = Buffer.from(encodedToken, "base64").toString("utf-8");
const data = JSON.parse(decoded) as CsrfTokenData;
if (
typeof data.token === "string" &&
typeof data.timestamp === "number"
) {
return data;
}
return null;
} catch {
return null;
}
}
/**
* Check if a CSRF token is expired
*/
function isTokenExpired(timestamp: number): boolean {
return Date.now() - timestamp > TOKEN_CONFIG.CSRF_TOKEN_EXPIRY_MS;
}
/**
* Hash a token for secure comparison
*/
function hashToken(token: string): string {
return createHash("sha256").update(token).digest("hex");
}
/**
* Validate a CSRF token
*
* @param headerToken - Token from X-CSRF-Token header
* @param cookieToken - Token from __csrf_token cookie
* @returns boolean indicating if tokens are valid and match
*/
export function validateCsrfToken(
headerToken: string | null,
cookieToken: string | null
): boolean {
if (!headerToken || !cookieToken) {
return false;
}
// Parse both tokens
const headerData = parseCsrfToken(headerToken);
const cookieData = parseCsrfToken(cookieToken);
if (!headerData || !cookieData) {
return false;
}
// Check expiry
if (isTokenExpired(headerData.timestamp) || isTokenExpired(cookieData.timestamp)) {
return false;
}
// Compare token hashes (timing-safe comparison via hash comparison)
const headerHash = hashToken(headerData.token);
const cookieHash = hashToken(cookieData.token);
return headerHash === cookieHash;
}
/**
* Set CSRF token cookie
*/
export async function setCsrfCookie(token: string): Promise<void> {
const cookieStore = await cookies();
cookieStore.set(CSRF_COOKIE_NAME, token, {
httpOnly: false, // Must be readable by JavaScript
secure: process.env.NODE_ENV === "production",
sameSite: "strict",
path: "/",
maxAge: Math.floor(TOKEN_CONFIG.CSRF_TOKEN_EXPIRY_MS / 1000)});
}
/**
* Get CSRF token from cookie
*/
export async function getCsrfTokenFromCookie(): Promise<string | null> {
const cookieStore = await cookies();
return cookieStore.get(CSRF_COOKIE_NAME)?.value || null;
}
/**
* Middleware helper to validate CSRF for state-changing requests
*
* @param request - NextRequest object
* @returns Object with validation result and optional error response
*/
export async function validateCsrfRequest(
request: NextRequest
): Promise<{ valid: boolean; error?: NextResponse }> {
// Only validate state-changing methods
if (["GET", "HEAD", "OPTIONS"].includes(request.method)) {
return { valid: true };
}
// Get token from header
const headerToken = request.headers.get(CSRF_HEADER_NAME);
// Get token from cookie
const cookieToken = request.cookies.get(CSRF_COOKIE_NAME)?.value || null;
// Validate tokens
if (!validateCsrfToken(headerToken, cookieToken)) {
return {
valid: false,
error: NextResponse.json(
{ error: "Invalid or missing CSRF token" },
{ status: 403 }
)};
}
return { valid: true };
}
/**
* Validate request origin to prevent CSRF from different origins
*
* @param request - NextRequest object
* @param allowedOrigins - List of allowed origins
* @returns boolean indicating if origin is valid
*/
export function validateOrigin(
request: NextRequest,
allowedOrigins?: string[]
): boolean {
const origin = request.headers.get("origin");
const referer = request.headers.get("referer");
// For same-origin requests, origin might be null
if (!origin && !referer) {
// Could be same-origin or a direct API call
// Be cautious but don't block entirely
return true;
}
const requestOrigin = origin || (referer ? new URL(referer).origin : null);
if (!requestOrigin) {
return true;
}
// Default allowed origins from environment
const defaultAllowed = process.env.NEXTAUTH_URL
? [new URL(process.env.NEXTAUTH_URL).origin]
: ["http://localhost:3000"];
const allowed = allowedOrigins || defaultAllowed;
return allowed.some((allowedOrigin) => {
try {
return new URL(allowedOrigin).origin === requestOrigin;
} catch {
return allowedOrigin === requestOrigin;
}
});
}
/**
* HOC wrapper for API routes requiring CSRF protection
*
* Usage:
* ```typescript
* import { withCsrfProtection } from "@/lib/auth";
*
* async function handler(request: NextRequest) {
* // Your handler code
* }
*
* export const POST = withCsrfProtection(handler);
* ```
*/
export function withCsrfProtection(
handler: (request: NextRequest) => Promise<NextResponse>
): (request: NextRequest) => Promise<NextResponse> {
return async (request: NextRequest) => {
const { valid, error } = await validateCsrfRequest(request);
if (!valid && error) {
return error;
}
return handler(request);
};
}
/**
* @deprecated Use NextAuth's built-in CSRF endpoint at /api/auth/csrf instead.
* This function is kept for backwards compatibility but should not be used
* for new implementations.
*
* NextAuth provides automatic CSRF protection for authentication flows.
* For custom API routes that need CSRF protection, use the
* `withCsrfProtection` HOC or `validateCsrfRequest` function instead.
*/
export async function getCsrfTokenResponse(): Promise<NextResponse> {
const token = generateCsrfToken();
await setCsrfCookie(token);
return NextResponse.json(
{ csrfToken: token },
{
status: 200,
headers: {
"Cache-Control": "no-store, no-cache, must-revalidate, proxy-revalidate",
Pragma: "no-cache",
Expires: "0"}}
);
}
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