fix(AppCheck): add siteKey validation and cleanup Package.swift

Author: ncooke3

FirebaseAppCheck/Sources/RecaptchaProvider/FIRAppCheckRecaptchaEnterpriseProviderFactory.m

@@ -28,6 +28,7 @@ @interface FIRAppCheckRecaptchaEnterpriseProviderFactory ()
 @implementation FIRAppCheckRecaptchaEnterpriseProviderFactory
 
 - (instancetype)initWithSiteKey:(NSString *)siteKey {
+  NSParameterAssert(siteKey.length > 0);
   self = [super init];
 
   if (self) {

FirebaseAppCheck/Sources/RecaptchaProvider/FIRRecaptchaEnterpriseProvider.m

@@ -48,7 +48,11 @@ - (instancetype)initWithRecaptchaEnterpriseProvider:
 }
 
 - (nullable instancetype)initWithApp:(FIRApp *)app siteKey:(NSString *)siteKey {
+  if (siteKey.length == 0) {
+    return nil;
+  }
   NSArray<NSString *> *missingOptionsFields =
+
       [FIRAppCheckValidator tokenExchangeMissingFieldsInOptions:app.options];
   if (missingOptionsFields.count > 0) {
     FIRLogError(kFIRLoggerAppCheck,

Package.swift

@@ -1264,8 +1264,8 @@ let package = Package(
               .product(name: "AppCheckCore", package: "app-check"),
               .product(name: "RecaptchaEnterpriseProvider", package: "app-check"),
               .product(name: "GULEnvironment", package: "GoogleUtilities"),
-
               .product(name: "GULUserDefaults", package: "GoogleUtilities"),
+
             ],
             path: "FirebaseAppCheck/Sources",
             publicHeadersPath: "Public",