feat: add DPoP sender-constrained token support (RFC 9449)

README.md

@@ -479,6 +479,50 @@ for more information.
 
 Note: if refresh token rotation is enabled in Descope - `refreshSession` / `validateAndRefreshSession` will return a new refresh token, and the old one will be invalidated.
 
+#### DPoP Sender-Constrained Tokens (RFC 9449)
+
+Descope supports DPoP (Demonstrated Proof of Possession) sender-constrained tokens. When a session
+token contains a `cnf.jkt` claim, the client must prove possession of the corresponding private key
+on every request by sending a `DPoP` header containing a signed proof JWT.
+
+After validating the session with `validateSession`, call `validateDPoP` to verify the DPoP proof:
+
+```typescript
+import descopeClient from '@descope/node-sdk';
+
+const sdk = descopeClient({ projectId: 'YOUR_PROJECT_ID' });
+
+// In your request handler:
+const sessionToken = req.headers.authorization?.replace(/^(Bearer|DPoP)\s+/i, '');
+const dpopProof = req.headers['dpop'] as string | undefined;
+
+// First validate the session token
+const authInfo = await sdk.validateSession(sessionToken);
+
+// Then validate the DPoP proof (no-op if token is not DPoP-bound)
+await sdk.validateDPoP(
+  authInfo.jwt,        // the raw session JWT string
+  dpopProof,           // value of the DPoP header
+  req.method,          // HTTP method in uppercase, e.g. "GET"
+  `https://${req.headers.host}${req.url}`, // absolute request URL
+);
+```
+
+If the token is DPoP-bound and the proof is missing or invalid, `validateDPoP` throws an error.
+If the token has no `cnf.jkt` claim (i.e. it is a regular Bearer token), `validateDPoP` is a no-op.
+
+The `DPoP` Authorization scheme is treated identically to `Bearer` — the session JWT that follows
+the scheme prefix is the same Descope-issued token in both cases.
+
+You can also import the standalone helpers directly:
+
+```typescript
+import { validateDPoPProof, getDPoPThumbprint } from '@descope/node-sdk';
+
+// Extract cnf.jkt from already-parsed token claims
+const jkt = getDPoPThumbprint(authInfo.token);
+```
+
 #### Session Validation Using Middleware
 
 Alternatively, you can create a simple middleware function that internally uses the `validateSession` function.

lib/dpop.ts

@@ -0,0 +1,240 @@
+import { createHash } from 'crypto';
+import { calculateJwkThumbprint, compactVerify, importJWK } from 'jose';
+
+/** Allowed DPoP proof signing algorithms per RFC 9449 */
+const ALLOWED_ALGS = new Set([
+  'RS256',
+  'RS384',
+  'RS512',
+  'ES256',
+  'ES384',
+  'ES512',
+  'PS256',
+  'PS384',
+  'PS512',
+  'EdDSA',
+]);
+
+/** Maximum DPoP proof JWT size in bytes */
+const MAX_PROOF_LEN = 8192;
+
+/** Backward clock skew tolerance in seconds */
+const IAT_BACKWARD_WINDOW = 60;
+
+/** Forward clock skew tolerance in seconds */
+const IAT_FORWARD_WINDOW = 5;
+
+/**
+ * Extract the DPoP JWK thumbprint from token claims.
+ * Returns an empty string if the token is not DPoP-bound.
+ */
+export function getDPoPThumbprint(claims: Record<string, unknown>): string {
+  const cnf = claims?.cnf as Record<string, unknown> | undefined;
+  return (cnf?.jkt as string) || '';
+}
+
+/**
+ * Normalize a URL for DPoP `htu` comparison per RFC 9449 §4.2:
+ * - Lowercase scheme and host
+ * - Strip default ports (443 for https, 80 for http)
+ * - Strip query string and fragment
+ */
+function normalizeHtu(raw: string): string {
+  let parsed: URL;
+  try {
+    parsed = new URL(raw);
+  } catch {
+    return '';
+  }
+  const scheme = parsed.protocol.replace(/:$/, '').toLowerCase();
+  const host = parsed.hostname.toLowerCase();
+  const port = parsed.port;
+  const defaultPort = scheme === 'https' ? '443' : scheme === 'http' ? '80' : '';
+
+  const portStr = port && port !== defaultPort ? `:${port}` : '';
+  return `${scheme}://${host}${portStr}${parsed.pathname}`;
+}
+
+/**
+ * Base64url-encode a buffer without padding characters.
+ */
+function base64urlNoPad(buf: Buffer): string {
+  return buf.toString('base64').replace(/\+/g, '-').replace(/\//g, '_').replace(/=/g, '');
+}
+
+/**
+ * Validate a DPoP proof JWT against the provided session token, HTTP method, and request URL.
+ *
+ * @param sessionToken - The validated session JWT string (used for `ath` claim verification)
+ * @param dpopProof - The value of the `DPoP` HTTP header from the incoming request
+ * @param method - HTTP method of the request, uppercase (e.g. "GET", "POST")
+ * @param requestUrl - Absolute URL of the request (e.g. "https://api.example.com/resource")
+ *
+ * @throws Error if DPoP validation fails for any reason
+ * @returns void — resolves successfully if the proof is valid, or is a no-op when the session
+ *   token has no `cnf.jkt` claim (i.e. is not DPoP-bound)
+ */
+export async function validateDPoPProof(
+  sessionToken: string,
+  dpopProof: string | undefined,
+  method: string,
+  requestUrl: string,
+): Promise<void> {
+  // Decode the session JWT claims to check for cnf.jkt (no signature verification needed here —
+  // the caller has already validated the session token via validateSession).
+  const parts = sessionToken.split('.');
+  if (parts.length < 2) return;
+  let claims: Record<string, unknown>;
+  try {
+    claims = JSON.parse(Buffer.from(parts[1], 'base64url').toString('utf8'));
+  } catch {
+    return;
+  }
+
+  const storedJKT = getDPoPThumbprint(claims);
+  if (!storedJKT) {
+    // Token is not DPoP-bound — nothing to validate
+    return;
+  }
+
+  // --- From here on, the token IS DPoP-bound. Proof is required. ---
+
+  const proof = (dpopProof ?? '').trim();
+
+  if (proof.length > MAX_PROOF_LEN) {
+    throw new Error('DPoP proof exceeds maximum length');
+  }
+
+  if (!proof) {
+    throw new Error(
+      'DPoP proof required: access token is DPoP-bound (cnf.jkt present)',
+    );
+  }
+
+  // Step 4-5: Parse protected header (first part of JWS compact serialization)
+  const proofParts = proof.split('.');
+  if (proofParts.length !== 3) {
+    throw new Error('DPoP proof must be a compact JWS with exactly 3 parts');
+  }
+
+  let header: Record<string, unknown>;
+  try {
+    header = JSON.parse(Buffer.from(proofParts[0], 'base64url').toString('utf8'));
+  } catch {
+    throw new Error('DPoP proof header is not valid base64url-encoded JSON');
+  }
+
+  // Step 6: typ must be "dpop+jwt"
+  if (header.typ !== 'dpop+jwt') {
+    throw new Error(`DPoP proof header typ must be "dpop+jwt", got "${header.typ}"`);
+  }
+
+  // Step 7: alg must be in ALLOWED_ALGS
+  const alg = header.alg as string;
+  if (!alg || !ALLOWED_ALGS.has(alg)) {
+    throw new Error(`DPoP proof algorithm "${alg}" is not allowed`);
+  }
+
+  // Step 8: extract embedded JWK
+  const jwk = header.jwk as Record<string, unknown>;
+  if (!jwk || typeof jwk !== 'object') {
+    throw new Error('DPoP proof header must contain a jwk claim');
+  }
+
+  // Step 9: no symmetric keys
+  if (jwk.kty === 'oct') {
+    throw new Error('DPoP proof JWK must not use symmetric key type (oct)');
+  }
+
+  // Step 10: no private key components
+  if ('d' in jwk) {
+    throw new Error('DPoP proof JWK must not contain private key components');
+  }
+
+  // Step 11: verify JWS signature using the embedded JWK
+  let payloadBytes: Uint8Array;
+  try {
+    const cryptoKey = await importJWK(jwk as Parameters<typeof importJWK>[0], alg);
+    const result = await compactVerify(proof, cryptoKey);
+    payloadBytes = result.payload;
+  } catch (err) {
+    throw new Error(`DPoP proof signature verification failed: ${err}`);
+  }
+
+  // Step 12: parse JWT payload
+  let payload: Record<string, unknown>;
+  try {
+    payload = JSON.parse(Buffer.from(payloadBytes).toString('utf8'));
+  } catch {
+    throw new Error('DPoP proof payload is not valid JSON');
+  }
+
+  // Steps 13-15: required string claims
+  if (!payload.jti || typeof payload.jti !== 'string') {
+    throw new Error('DPoP proof payload must contain a non-empty string jti claim');
+  }
+  if (!payload.htm || typeof payload.htm !== 'string') {
+    throw new Error('DPoP proof payload must contain a non-empty string htm claim');
+  }
+  if (!payload.htu || typeof payload.htu !== 'string') {
+    throw new Error('DPoP proof payload must contain a non-empty string htu claim');
+  }
+
+  // Step 16: htm must match the HTTP method
+  if (payload.htm !== method) {
+    throw new Error(
+      `DPoP proof htm "${payload.htm}" does not match request method "${method}"`,
+    );
+  }
+
+  // Step 17: htu must match the request URL (scheme+host+path, ignore query/fragment)
+  const normalizedHtu = normalizeHtu(payload.htu as string);
+  const normalizedUrl = normalizeHtu(requestUrl);
+  if (!normalizedHtu || !normalizedUrl || normalizedHtu !== normalizedUrl) {
+    throw new Error(
+      `DPoP proof htu "${payload.htu}" does not match request URL "${requestUrl}"`,
+    );
+  }
+
+  // Steps 18-21: iat window check (no exp in DPoP proofs)
+  const iat = payload.iat;
+  if (typeof iat !== 'number') {
+    throw new Error('DPoP proof payload must contain a numeric iat claim');
+  }
+  const now = Date.now() / 1000;
+  const diff = now - iat;
+  if (diff <= -IAT_FORWARD_WINDOW || diff >= IAT_BACKWARD_WINDOW) {
+    throw new Error(
+      `DPoP proof iat is outside the acceptable window (diff=${diff.toFixed(2)}s)`,
+    );
+  }
+
+  // Steps 22-24: ath claim — sha256(sessionToken) as base64url without padding
+  const ath = payload.ath;
+  if (!ath || typeof ath !== 'string') {
+    throw new Error('DPoP proof payload must contain a non-empty string ath claim');
+  }
+  const expectedAth = base64urlNoPad(
+    createHash('sha256').update(sessionToken).digest(),
+  );
+  if (ath !== expectedAth) {
+    throw new Error('DPoP proof ath claim does not match the session token hash');
+  }
+
+  // Steps 25-26: JWK thumbprint must match cnf.jkt in the session token
+  let thumbprint: string;
+  try {
+    thumbprint = await calculateJwkThumbprint(
+      jwk as Parameters<typeof calculateJwkThumbprint>[0],
+      'sha256',
+    );
+  } catch (err) {
+    throw new Error(`Failed to compute DPoP JWK thumbprint: ${err}`);
+  }
+
+  if (thumbprint !== storedJKT) {
+    throw new Error(
+      `DPoP proof JWK thumbprint "${thumbprint}" does not match session cnf.jkt "${storedJKT}"`,
+    );
+  }
+}

lib/index.ts

@@ -26,6 +26,7 @@ import withManagement from './management';
 import withLicense from './management/license';
 import { AuthenticationInfo, IDPResponse, RefreshAuthenticationInfo, VerifyOptions } from './types';
 import descopeErrors from './errors';
+import { validateDPoPProof, getDPoPThumbprint } from './dpop';
 
 declare const BUILD_VERSION: string;
 
@@ -361,6 +362,27 @@ const nodeSdk = ({
       }
     },
 
+    /**
+     * Validate a DPoP proof JWT for a DPoP-bound session token (RFC 9449).
+     *
+     * Call this after `validateSession` when your server receives requests that may carry
+     * a `DPoP` header. If the session token does not have a `cnf.jkt` claim this is a no-op.
+     *
+     * @param sessionToken - The validated session JWT string returned by `validateSession`
+     * @param dpopProof - The value of the `DPoP` header from the incoming request
+     * @param method - HTTP method of the request in uppercase, e.g. `"GET"` or `"POST"`
+     * @param requestUrl - Absolute URL of the request, e.g. `"https://api.example.com/resource"`
+     * @throws Error if the DPoP proof is missing, invalid, or does not match the session token
+     */
+    async validateDPoP(
+      sessionToken: string,
+      dpopProof: string | undefined,
+      method: string,
+      requestUrl: string,
+    ): Promise<void> {
+      return validateDPoPProof(sessionToken, dpopProof, method, requestUrl);
+    },
+
     /**
      * Make sure that all given permissions exist on the parsed JWT top level claims
      * @param authInfo JWT parsed info
@@ -530,3 +552,4 @@ export type { AuthenticationInfo, IDPResponse, RefreshAuthenticationInfo };
 export type { VerifyOptions } from './types';
 export * from './management/types';
 export type { PatchUserOptions } from './management/user';
+export { validateDPoPProof, getDPoPThumbprint } from './dpop';