Allow JWT::decode to accept an empty string as a valid kid

src/JWT.php

@@ -465,17 +465,15 @@ private static function getKey(
         $keyOrKeyArray,
         ?string $kid
     ): Key {
+
+        $kid = (string) $kid;
+
         if ($keyOrKeyArray instanceof Key) {
             return $keyOrKeyArray;
         }
 
-        if (empty($kid) && $kid !== '0') {
-            throw new UnexpectedValueException('"kid" empty, unable to lookup correct key');
-        }
-
-        if ($keyOrKeyArray instanceof CachedKeySet) {
-            // Skip "isset" check, as this will automatically refresh if not set
-            return $keyOrKeyArray[$kid];
+        if (!is_array($keyOrKeyArray) && !$keyOrKeyArray instanceof ArrayAccess) {
+            throw new UnexpectedValueException('Expecting a Key or an associative array of keys');
         }
 
         if (!isset($keyOrKeyArray[$kid])) {

tests/JWTTest.php

@@ -327,6 +327,19 @@ public function testKIDChooser()
         $this->assertEquals($decoded, $expected);
     }
 
+    public function testArrayAccessKIDChooserWhenJWTHasNoKey()
+    {
+        $key = new Key('my_key0', 'HS256');
+        $keys = new ArrayObject([
+            '' => $key,
+        ]);
+        $msg = JWT::encode(['message' => 'abc'], $key->getKeyMaterial(), 'HS256');
+        $decoded = JWT::decode($msg, $keys);
+        $expected = new stdClass();
+        $expected->message = 'abc';
+        $this->assertEquals($decoded, $expected);
+    }
+
     public function testArrayAccessKIDChooser()
     {
         $keys = new ArrayObject([
@@ -383,6 +396,26 @@ public function testInvalidSignatureEncoding()
         JWT::decode($msg, new Key('secret', 'HS256'));
     }
 
+    public function testInvalideKeyOrKeyArray()
+    {
+        $key = 'yma6Hq4XQegCVND8ef23OYgxSrC3IKqk';
+        $payload = ['foo' => [1, 2, 3]];
+        $jwt = JWT::encode($payload, $key, 'HS256');
+        $this->expectException(UnexpectedValueException::class);
+        $this->expectExceptionMessage('Expecting a Key or an associative array of keys');
+        JWT::decode($jwt, 'SomeKeyNotAnArray');
+    }
+
+    public function testKeyNotInKeyOrKeyArray()
+    {
+        $key = 'yma6Hq4XQegCVND8ef23OYgxSrC3IKqk';
+        $payload = ['foo' => [1, 2, 3]];
+        $jwt = JWT::encode($payload, $key, 'HS256');
+        $this->expectException(UnexpectedValueException::class);
+        $this->expectExceptionMessage('"kid" invalid, unable to lookup correct key');
+        JWT::decode($jwt, ['notrealkey' => 'SomeKeyNotAnArray']);
+    }
+
     public function testHSEncodeDecode()
     {
         $msg = JWT::encode(['message' => 'abc'], 'my_key', 'HS256');