feat: add defaultAlg param

src/CachedKeySet.php

@@ -68,21 +68,27 @@ class CachedKeySet implements ArrayAccess
      * @var int
      */
     private $maxCallsPerMinute = 10;
+    /**
+     * @var string|null
+     */
+    private $defaultAlg;
 
     public function __construct(
         string $jwksUri,
         ClientInterface $httpClient,
         RequestFactoryInterface $httpFactory,
         CacheItemPoolInterface $cache,
         int $expiresAfter = null,
-        bool $rateLimit = false
+        bool $rateLimit = false,
+        string $defaultAlg = null
     ) {
         $this->jwksUri = $jwksUri;
         $this->httpClient = $httpClient;
         $this->httpFactory = $httpFactory;
         $this->cache = $cache;
         $this->expiresAfter = $expiresAfter;
         $this->rateLimit = $rateLimit;
+        $this->defaultAlg = $defaultAlg;
         $this->setCacheKeys();
     }
 
@@ -143,7 +149,7 @@ private function keyIdExists(string $keyId): bool
             $request = $this->httpFactory->createRequest('get', $this->jwksUri);
             $jwksResponse = $this->httpClient->sendRequest($request);
             $jwks = json_decode((string) $jwksResponse->getBody(), true);
-            $this->keySet = $keySetToCache = JWK::parseKeySet($jwks);
+            $this->keySet = $keySetToCache = JWK::parseKeySet($jwks, $this->defaultAlg);
 
             if (!isset($this->keySet[$keyId])) {
                 return false;

src/JWK.php

@@ -24,6 +24,8 @@ class JWK
      * Parse a set of JWK keys
      *
      * @param array<mixed> $jwks The JSON Web Key Set as an associative array
+     * @param string       $defaultAlg The algorithm for the Key object if "alg" is not set in the
+     *                                 JSON Web Key Set
      *
      * @return array<string, Key> An associative array of key IDs (kid) to Key objects
      *
@@ -33,7 +35,7 @@ class JWK
      *
      * @uses parseKey
      */
-    public static function parseKeySet(array $jwks): array
+    public static function parseKeySet(array $jwks, string $defaultAlg = null): array
     {
         $keys = [];
 
@@ -47,7 +49,7 @@ public static function parseKeySet(array $jwks): array
 
         foreach ($jwks['keys'] as $k => $v) {
             $kid = isset($v['kid']) ? $v['kid'] : $k;
-            if ($key = self::parseKey($v)) {
+            if ($key = self::parseKey($v, $defaultAlg)) {
                 $keys[(string) $kid] = $key;
             }
         }
@@ -63,6 +65,8 @@ public static function parseKeySet(array $jwks): array
      * Parse a JWK key
      *
      * @param array<mixed> $jwk An individual JWK
+     * @param string       $defaultAlg The algorithm for the Key object if "alg" is not set in the
+     *                                 JSON Web Key Set
      *
      * @return Key The key object for the JWK
      *
@@ -72,7 +76,7 @@ public static function parseKeySet(array $jwks): array
      *
      * @uses createPemFromModulusAndExponent
      */
-    public static function parseKey(array $jwk): ?Key
+    public static function parseKey(array $jwk, string $defaultAlg = null): ?Key
     {
         if (empty($jwk)) {
             throw new InvalidArgumentException('JWK must not be empty');
@@ -83,10 +87,14 @@ public static function parseKey(array $jwk): ?Key
         }
 
         if (!isset($jwk['alg'])) {
-            // The "alg" parameter is optional in a KTY, but is required for parsing in
-            // this library. Add it manually to your JWK array if it doesn't already exist.
-            // @see https://datatracker.ietf.org/doc/html/rfc7517#section-4.4
-            throw new UnexpectedValueException('JWK must contain an "alg" parameter');
+            if (\is_null($defaultAlg)) {
+                // The "alg" parameter is optional in a KTY, but an algorithm is required
+                // for parsing in this library. Use the $defaultAlg parameter when parsing the
+                // key set in order to prevent this error.
+                // @see https://datatracker.ietf.org/doc/html/rfc7517#section-4.4
+                throw new UnexpectedValueException('JWK must contain an "alg" parameter');
+            }
+            $jwk['alg'] = $defaultAlg;
         }
 
         switch ($jwk['kty']) {

tests/CachedKeySetTest.php

@@ -18,6 +18,7 @@ class CachedKeySetTest extends TestCase
     private $testJwksUriKey = 'jwkshttpsjwk.uri';
     private $testJwks1 = '{"keys": [{"kid":"foo","kty":"RSA","alg":"foo","n":"","e":""}]}';
     private $testJwks2 = '{"keys": [{"kid":"bar","kty":"RSA","alg":"bar","n":"","e":""}]}';
+    private $testJwks3 = '{"keys": [{"kid":"baz","kty":"RSA","n":"","e":""}]}';
 
     private $googleRsaUri = 'https://www.googleapis.com/oauth2/v3/certs';
     // private $googleEcUri = 'https://www.gstatic.com/iap/verify/public_key-jwk';
@@ -95,6 +96,21 @@ public function testWithExistingKeyId()
         $this->assertEquals('foo', $cachedKeySet['foo']->getAlgorithm());
     }
 
+    public function testWithDefaultAlg()
+    {
+        $cachedKeySet = new CachedKeySet(
+            $this->testJwksUri,
+            $this->getMockHttpClient($this->testJwks3),
+            $this->getMockHttpFactory(),
+            $this->getMockEmptyCache(),
+            null,
+            false,
+            'baz256'
+        );
+        $this->assertInstanceOf(Key::class, $cachedKeySet['baz']);
+        $this->assertEquals('baz256', $cachedKeySet['baz']->getAlgorithm());
+    }
+
     public function testKeyIdIsCached()
     {
         $cacheItem = $this->prophesize(CacheItemInterface::class);

tests/JWKTest.php

@@ -58,6 +58,18 @@ public function testParsePrivateKeyWithoutAlg()
         JWK::parseKeySet($jwkSet);
     }
 
+    public function testParsePrivateKeyWithoutAlgWithDefaultAlgParameter()
+    {
+        $jwkSet = json_decode(
+            file_get_contents(__DIR__ . '/data/rsa-jwkset.json'),
+            true
+        );
+        unset($jwkSet['keys'][0]['alg']);
+
+        $jwks = JWK::parseKeySet($jwkSet, 'foo');
+        $this->assertEquals('foo', $jwks['jwk1']->getAlgorithm());
+    }
+
     public function testParseKeyWithEmptyDValue()
     {
         $jwkSet = json_decode(