OIDC の ID トークン検証を手順ごとに解説

import { createHash } from "node:crypto";
import { jwtVerify } from "jose";

// at_hash and c_hash: the left half of the hash of the ASCII value, base64url-encoded,
// with the hash function of the ID token's alg (OIDC Core 3.1.3.6 and 3.3.2.11).
const HASH = { RS256: "sha256", PS256: "sha256", ES256: "sha256", RS384: "sha384", PS384: "sha384", ES384: "sha384", RS512: "sha512", PS512: "sha512", ES512: "sha512" };
export function halfHash(value, alg) {
  const digest = createHash(HASH[alg]).update(value, "ascii").digest();
  return digest.subarray(0, digest.length / 2).toString("base64url");
}

/**
 * Validates an ID token as OpenID Connect Core 1.0 §3.1.3.7 describes.
 * rp:       { issuer, jwks, clientId, alg, trustedAudiences, trustedPresenters, maxIatAgeSeconds }
 * expected: { nonce, maxAge?, accessToken?, code? } from this login's stored state and the response
 */
export async function validateIdToken(idToken, rp, expected) {
  // Steps 2, 3 (aud contains client_id), 6, 7 and 9: issuer, audience, signature, alg, expiry.
  const { payload: claims, protectedHeader } = await jwtVerify(idToken, rp.jwks, {
    issuer: rp.issuer, // exact string from the discovery document
    audience: rp.clientId,
    algorithms: [rp.alg], // RS256 unless id_token_signed_response_alg says otherwise
    requiredClaims: ["iss", "sub", "aud", "exp", "iat"],
    clockTolerance: 30,
  });
  const now = Math.floor(Date.now() / 1000);
  const fail = (step, why) => {
    throw new Error(`step ${step}: ${why}`);
  };

  // Step 3, second half: reject audiences this client does not trust.
  const untrusted = [claims.aud].flat().filter((a) => a !== rp.clientId && !rp.trustedAudiences.includes(a));
  if (untrusted.length > 0) fail(3, `untrusted audience ${untrusted.join(", ")}`);
  // Steps 4-5: an azp, when present, must name a client of this application.
  if (claims.azp !== undefined && ![rp.clientId, ...rp.trustedPresenters].includes(claims.azp)) {
    fail(5, `azp is ${claims.azp}`);
  }
  // Step 10: iat bounds how long nonces must be remembered.
  if (now - claims.iat > rp.maxIatAgeSeconds) fail(10, `issued ${now - claims.iat} s ago`);
  // Step 11: the nonce stored with this login attempt, compared exactly.
  if (claims.nonce !== expected.nonce) fail(11, `nonce ${claims.nonce} does not match the stored value`);
  // Step 13: when max_age was sent, auth_time is required and bounded.
  if (expected.maxAge !== undefined) {
    if (typeof claims.auth_time !== "number") fail(13, "auth_time missing");
    if (now - claims.auth_time > expected.maxAge + 30) fail(13, "authentication too old");
  }
  // Hashes: tie the access token (at_hash) and the code (c_hash) to this ID token.
  if (expected.accessToken !== undefined && claims.at_hash !== undefined) {
    if (claims.at_hash !== halfHash(expected.accessToken, protectedHeader.alg)) fail("3.1.3.8", "at_hash mismatch");
  }
  if (expected.code !== undefined) {
    if (claims.c_hash !== halfHash(expected.code, protectedHeader.alg)) fail("3.3.2.10", "c_hash missing or mismatch");
  }
  return claims;
}

issuer http://127.0.0.1:8080/realms/demo
code flow callback parameters: state, session_state, iss, code
ID token header: alg RS256, typ JWT, kid present: true
ID token claims: exp, iat, auth_time, jti, iss, aud, sub, typ, azp, nonce, sid, at_hash, acr, email_verified, name, preferred_username, given_name, family_name, email
aud "web-app", azp web-app, at_hash present
code flow ID token                                   valid
hybrid callback parameters: state, session_state, iss, code, id_token
front-channel ID token: c_hash present, at_hash absent
hybrid front-channel ID token, with its code         valid
same ID token, code from the first login             rejected: step 3.3.2.10: c_hash missing or mismatch
other-app ID token: aud ["other-app","web-app"], azp other-app
other-app token, aud-contains check only             valid
other-app token, full validation                     rejected: step 3: untrusted audience other-app
first ID token, nonce of the second login            rejected: step 11: nonce lsamKJG6vC-xAIOzo1LIrw does not match the stored value
first ID token, access token of the second login     rejected: step 3.1.3.8: at_hash mismatch

// The library route: openid-client 6.8.8 runs discovery, the code exchange and the ID token checks.
import * as client from "openid-client";
import { browserLogin } from "./login.mjs";

const issuer = new URL("http://127.0.0.1:8080/realms/demo");
// allowInsecureRequests only because the lab issuer is plain http; never in production.
const config = await client.discovery(issuer, "web-app", process.env.WEB, undefined, {
  execute: [client.allowInsecureRequests],
});

async function signIn(expectedNonceOverride) {
  const codeVerifier = client.randomPKCECodeVerifier();
  const state = client.randomState();
  const nonce = client.randomNonce();
  const url = client.buildAuthorizationUrl(config, {
    redirect_uri: "http://127.0.0.1:3000/callback",
    scope: "openid email",
    code_challenge: await client.calculatePKCECodeChallenge(codeVerifier),
    code_challenge_method: "S256",
    state,
    nonce,
  });
  const { location } = await browserLogin(url, "alice", process.env.PW);
  const tokens = await client.authorizationCodeGrant(config, new URL(location), {
    pkceCodeVerifier: codeVerifier,
    expectedState: state,
    expectedNonce: expectedNonceOverride ?? nonce,
    idTokenExpected: true,
  });
  return tokens.claims();
}

const claims = await signIn();
console.log(`signed in: sub ${claims.sub.slice(0, 8)}..., email ${claims.email}, nonce checked`);
try {
  await signIn(client.randomNonce());
} catch (e) {
  console.log(`wrong expectedNonce: ${e.name}: ${e.message}; cause: ${e.cause?.message}`);
}

signed in: sub aa5e60df..., email alice@example.com, nonce checked
wrong expectedNonce: ClientError: unexpected JWT claim value encountered; cause: unexpected ID Token "nonce" claim value

package main

// What go-oidc's IDTokenVerifier checks on its own, against ID tokens from the lab Keycloak realm.

import (
	"context"
	"encoding/json"
	"fmt"
	"os"

	"github.com/coreos/go-oidc/v3/oidc"
)

func main() {
	var h struct {
		Issuer, IDToken, AccessToken, NonceSent, NonceOfAnotherLogin, OtherAppIDToken, OtherAccessToken string
	}
	data, _ := os.ReadFile("/node/handoff.json")
	if err := json.Unmarshal(data, &h); err != nil {
		panic(err)
	}
	ctx := context.Background()
	ctx = oidc.InsecureIssuerURLContext(ctx, h.Issuer) // only because the lab issuer is plain http
	provider, err := oidc.NewProvider(ctx, h.Issuer)
	if err != nil {
		panic(err)
	}
	verifier := provider.Verifier(&oidc.Config{ClientID: "web-app"})

	token, err := verifier.Verify(ctx, h.IDToken)
	fmt.Printf("%-44s err=%v\n", "Verify(web-app ID token)", err)
	fmt.Printf("%-44s %v\n", "  nonce equals the nonce we sent", token.Nonce == h.NonceSent)
	fmt.Printf("%-44s %v\n", "  nonce equals another login's nonce", token.Nonce == h.NonceOfAnotherLogin)
	fmt.Printf("%-44s err=%v\n", "  VerifyAccessToken(its access token)", token.VerifyAccessToken(h.AccessToken))
	fmt.Printf("%-44s err=%v\n", "  VerifyAccessToken(another access token)", token.VerifyAccessToken(h.OtherAccessToken))

	other, err := verifier.Verify(ctx, h.OtherAppIDToken)
	if err == nil {
		var c struct {
			Azp string `json:"azp"`
		}
		_ = other.Claims(&c)
		fmt.Printf("%-44s err=<nil>, aud=%v, azp=%s\n", "Verify(other-app ID token)", other.Audience, c.Azp)
	} else {
		fmt.Printf("%-44s err=%v\n", "Verify(other-app ID token)", err)
	}
}

Verify(web-app ID token)                     err=<nil>
  nonce equals the nonce we sent             true
  nonce equals another login's nonce         false
  VerifyAccessToken(its access token)        err=<nil>
  VerifyAccessToken(another access token)    err=access token hash does not match value in ID token
Verify(other-app ID token)                   err=<nil>, aud=[other-app web-app], azp=other-app

# Prints issuer, jwks_uri and ID token signing algorithms from public OpenID Connect discovery documents.
import json
import urllib.request

URLS = [
    "https://accounts.google.com/.well-known/openid-configuration",
    "https://login.microsoftonline.com/common/v2.0/.well-known/openid-configuration",
    "https://login.microsoftonline.com/common/.well-known/openid-configuration",
    "https://samples.auth0.com/.well-known/openid-configuration",
    "https://appleid.apple.com/.well-known/openid-configuration",
]
for url in URLS:
    with urllib.request.urlopen(url, timeout=20) as response:
        doc = json.load(response)
    print(f"== {url}")
    print(f"   issuer   {doc['issuer']}")
    print(f"   jwks_uri {doc['jwks_uri']}")
    print(f"   id_token_signing_alg_values_supported {doc.get('id_token_signing_alg_values_supported')}")

== https://accounts.google.com/.well-known/openid-configuration
   issuer   https://accounts.google.com
   jwks_uri https://www.googleapis.com/oauth2/v3/certs
   id_token_signing_alg_values_supported ['RS256']
== https://login.microsoftonline.com/common/v2.0/.well-known/openid-configuration
   issuer   https://login.microsoftonline.com/{tenantid}/v2.0
   jwks_uri https://login.microsoftonline.com/common/discovery/v2.0/keys
   id_token_signing_alg_values_supported ['RS256']
== https://login.microsoftonline.com/common/.well-known/openid-configuration
   issuer   https://sts.windows.net/{tenantid}/
   jwks_uri https://login.microsoftonline.com/common/discovery/keys
   id_token_signing_alg_values_supported ['RS256']
== https://samples.auth0.com/.well-known/openid-configuration
   issuer   https://samples.auth0.com/
   jwks_uri https://samples.auth0.com/.well-known/jwks.json
   id_token_signing_alg_values_supported ['HS256', 'RS256', 'PS256']
== https://appleid.apple.com/.well-known/openid-configuration
   issuer   https://appleid.apple.com
   jwks_uri https://appleid.apple.com/auth/keys
   id_token_signing_alg_values_supported ['RS256']