Implemented phase 4 for the POC prototype in the Website service.

Services/Website/Sources/Library/Public/Extensions/ConfigKey+Constants.swift

@@ -99,6 +99,11 @@ extension ConfigKey {
         public static let strictTransportSecurity: ConfigKey = "security.strictTransportSecurity"
     }
     /// A namespace for the site configuration keys.
+    /// A namespace for the passkey configuration keys.
+    public enum Passkeys {
+        /// The configuration key for the origin the sign-in screen is served at, which passkeys are bound to.
+        public static let origin: ConfigKey = "passkeys.origin"
+    }
     public enum Site {
         /// The configuration key for the public origin the site is served at (scheme and host, no trailing slash).
         public static let origin: ConfigKey = "site.origin"