REF-11 Harden metadata directory handling (#25, #24)

src/dk.nita.saml20/dk.nita.saml20/Config/SAML20FederationConfig.cs

@@ -479,6 +479,8 @@ private void HandleDeleteIdp(string filename)
         private void HandleUpdateIdp(string filename)
         {
             var metadataDoc = ParseFile(filename);
+            if (metadataDoc == null)
+                return; // Not a SAML 2.0 metadata file - ignore it instead of failing.
             // First we try and find the endpoint based on the entity id in the metadata
             var endp = FindEndPoint(metadataDoc.EntityId);
             if (endp == null && _fileToEntity.ContainsKey(filename))
@@ -501,6 +503,8 @@ private void HandleCreateIdp(string filename)
             if (!_fileToEntity.ContainsKey(filename))
             {
                 var metadataDoc = ParseFile(filename);
+                if (metadataDoc == null)
+                    return; // Not a SAML 2.0 metadata file (e.g. a README placed in the metadata directory) - ignore it instead of failing.
                 var endp = FindEndPoint(metadataDoc.EntityId);
                 if (endp == null) // If the endpoint does not exist, create it.
                 {

src/dk.nita.saml20/dk.nita.saml20/Properties/Resources.resx

@@ -334,7 +334,7 @@ AppID={1}</value>
     <value>The specified metadata directory "{0}" could not be located.</value>
   </data>
   <data name="MetadataNotFound" xml:space="preserve">
-    <value>Metadata not found for idp endpoint with id {0}</value>
+    <value>No metadata was found for the configured IDPEndpoint with id "{0}". Verify that the id matches the entityID of a metadata file in the configured metadata directory (a misspelled id is the most common cause).</value>
   </data>
   <data name="NoAttributeValuePresent" xml:space="preserve">
     <value>Xml error: attribute {0} of element {1}: {2} must have a value.</value>

src/dk.nita.saml20/dk.nita.saml20/Protocol/Saml20AbstractEndpointHandler.cs

@@ -9,6 +9,7 @@
 using dk.nita.saml20.Properties;
 using dk.nita.saml20.Schema.Protocol;
 using dk.nita.saml20.Utils;
+using Saml2.Properties;
 using Trace = dk.nita.saml20.Utils.Trace;
 
 namespace dk.nita.saml20.protocol
@@ -142,6 +143,11 @@ public IDPEndPoint RetrieveIDP(HttpContext context)
             var defaultIdp = config.Endpoints.IDPEndPoints.Find(idp => idp.Default);
             if (defaultIdp != null)
             {
+                // A configured endpoint has no metadata when no metadata file matches its id (typically a misspelled
+                // id). Fail with a clear message instead of the opaque NullReferenceException that follows downstream.
+                if (defaultIdp.metadata == null)
+                    throw new Saml20Exception(string.Format(Resources.MetadataNotFound, defaultIdp.Id));
+
                 if (Trace.ShouldTrace(TraceEventType.Information))
                     Trace.TraceData(TraceEventType.Information, "Using IdP marked as default: " + defaultIdp.Id);