feat: implement web service

Signed-off-by: The one with the braid <info@braid.business>

lib/pkpass/models/pass_web_service.dart

@@ -0,0 +1,31 @@
+/// Metadata required for Pass Web Service
+///
+/// https://developer.apple.com/library/archive/documentation/PassKit/Reference/PassKit_WebService/WebService.html#//apple_ref/doc/uid/TP40011988
+class PassWebService {
+  /// The authentication token to use with the web service.
+  /// The token must be 16 characters or longer.
+  final String authenticationToken;
+
+  /// The URL of a web service that conforms to the API described in PassKit Web Service Reference.
+  final Uri webServiceURL;
+
+  const PassWebService({
+    required this.authenticationToken,
+    required this.webServiceURL,
+  });
+
+  /// returns a [PassWebService] in case [authenticationToken] and
+  /// [webServiceURL] are both valid values.
+  static PassWebService? maybe({
+    String? authenticationToken,
+    String? webServiceURL,
+  }) {
+    if (authenticationToken == null || webServiceURL == null) return null;
+    final uri = Uri.tryParse(webServiceURL);
+    if (uri == null || uri.scheme != 'https') return null;
+    return PassWebService(
+      authenticationToken: authenticationToken,
+      webServiceURL: uri,
+    );
+  }
+}