Refactored Credential et al so that the security package is provided by name (string), and not an enum. Security packages are runtime enumerable, and new ones may be created that we don't have any idea of.

NSspi/Credentials/Credential.cs

@@ -16,13 +16,13 @@ namespace NSspi.Credentials
     {
         private bool disposed;
 
-        private SecurityPackage securityPackage;
+        private string securityPackage;
 
         private SafeCredentialHandle safeCredHandle;
 
         private DateTime expiry;
 
-        public Credential( SecurityPackage package )
+        public Credential( string package )
         {
             this.disposed = false;
             this.securityPackage = package;
@@ -35,7 +35,7 @@ namespace NSspi.Credentials
             Dispose( false );
         }
 
-        public SecurityPackage SecurityPackage
+        public string SecurityPackage
         {
             get
             {