Issue #3450693 by ptmkenny: Add validateToken() method

src/FirebasePhpMessagingApiInterface.php

@@ -119,4 +119,15 @@ interface FirebasePhpMessagingApiInterface {
     ?int $badge_count = NULL,
   ): MulticastSendReport;
 
+  /**
+   * Validates a registration token with Google's servers.
+   *
+   * @param string $token
+   *   The registration token to validate.
+   *
+   * @return bool
+   *   TRUE if the token is valid. FALSE if not.
+   */
+  public function validateToken(string $token): bool;
+
 }

src/Service/FirebasePhpMessagingApi.php

@@ -213,4 +213,22 @@ class FirebasePhpMessagingApi extends FirebasePhpMessagingService implements Fir
     }
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function validateToken(string $token): bool {
+    if (trim($token) === '') {
+      throw new FirebasePhpInvalidArgumentException('Token cannot be an empty string!');
+    }
+    /** @var non-empty-string $token */
+    $messaging_service = $this->getMessaging();
+    $output = $messaging_service->validateRegistrationTokens($token);
+    // We are only validating one token, so if there is a single invalid result,
+    // the token is invalid.
+    if (isset($output['invalid'][0])) {
+      return FALSE;
+    }
+    return TRUE;
+  }
+
 }