diff --git a/src/Sustainsys.Saml2.AspNetCore/ServiceResolver.cs b/src/Sustainsys.Saml2.AspNetCore/ServiceResolver.cs
index d532afa7e..498f1af5d 100644
--- a/src/Sustainsys.Saml2.AspNetCore/ServiceResolver.cs
+++ b/src/Sustainsys.Saml2.AspNetCore/ServiceResolver.cs
@@ -11,6 +11,10 @@
 
 namespace Sustainsys.Saml2.AspNetCore;
 
+// TODO: Replace with .NET 8 keyed services
+// Resolve services from key (= scheme) first, then fallback to
+// normal registration. Add default service implementations as singletons to DI.
+
 /// <summary>
 /// The Sustainsys.Saml2 library uses multiple loosely coupled services internally. The 
 /// default implementation is to not register these in the main dependency injection 
@@ -63,6 +67,7 @@ public class ResolverContext(
     public Func<ResolverContext, Saml2Events> CreateEvents { get; set; }
         = _ => new Saml2Events();
 
+    // TODO: Can this be a shared instance?
     /// <summary>
     /// Factory for <see cref="ISamlXmlReader"/>
     /// </summary>
diff --git a/src/Sustainsys.Saml2/Serialization/ISamlXmlReader.cs b/src/Sustainsys.Saml2/Serialization/ISamlXmlReader.cs
index 82df938ac..b9277f83a 100644
--- a/src/Sustainsys.Saml2/Serialization/ISamlXmlReader.cs
+++ b/src/Sustainsys.Saml2/Serialization/ISamlXmlReader.cs
@@ -47,5 +47,7 @@ public interface ISamlXmlReader
     /// <param name="source">Xml Traverser to read from</param>
     /// <param name="errorInspector">Callback that can inspect and alter errors before throwing</param>
     /// <returns><see cref="AuthnRequest"/></returns>
-    AuthnRequest ReadAuthnRequest(XmlTraverser source, Action<AuthnRequest, IList<Error>>? errorInspector = null);
+    AuthnRequest ReadAuthnRequest(
+        XmlTraverser source,
+        Action<ReadErrorInspectorContext<AuthnRequest>>? errorInspector = null);
 }
diff --git a/src/Sustainsys.Saml2/Serialization/SamlXmlReader.AuthnRequest.cs b/src/Sustainsys.Saml2/Serialization/SamlXmlReader.AuthnRequest.cs
index 76115a0ad..906a32976 100644
--- a/src/Sustainsys.Saml2/Serialization/SamlXmlReader.AuthnRequest.cs
+++ b/src/Sustainsys.Saml2/Serialization/SamlXmlReader.AuthnRequest.cs
@@ -1,5 +1,6 @@
 using Sustainsys.Saml2.Samlp;
 using Sustainsys.Saml2.Xml;
+using System.Xml;
 using static Sustainsys.Saml2.Constants;
 
 namespace Sustainsys.Saml2.Serialization;
@@ -14,12 +15,14 @@ public partial class SamlXmlReader
     //TODO: Convert other reads to follow this pattern with a callback for errors
 
     /// <inheritdoc/>
-    public virtual AuthnRequest ReadAuthnRequest(
+    public AuthnRequest ReadAuthnRequest(
         XmlTraverser source,
-        Action<AuthnRequest, IList<Error>>? errorInspector = null)
+        Action<ReadErrorInspectorContext<AuthnRequest>>? errorInspector = null)
     {
         var authnRequest = ReadAuthnRequest(source);
 
+        CallErrorInspector(errorInspector, authnRequest, source);
+
         source.ThrowOnErrors();
 
         return authnRequest;
diff --git a/src/Sustainsys.Saml2/Serialization/SamlXmlReader.cs b/src/Sustainsys.Saml2/Serialization/SamlXmlReader.cs
index ad0e8a60d..f427d1036 100644
--- a/src/Sustainsys.Saml2/Serialization/SamlXmlReader.cs
+++ b/src/Sustainsys.Saml2/Serialization/SamlXmlReader.cs
@@ -1,5 +1,6 @@
 using Sustainsys.Saml2.Common;
 using Sustainsys.Saml2.Saml;
+using Sustainsys.Saml2.Samlp;
 using Sustainsys.Saml2.Xml;
 using System;
 using System.Collections.Generic;
@@ -8,6 +9,7 @@
 using System.Security.Cryptography.Xml;
 using System.Text;
 using System.Threading.Tasks;
+using System.Xml;
 using static Sustainsys.Saml2.Constants;
 
 namespace Sustainsys.Saml2.Serialization;
@@ -79,4 +81,21 @@ protected virtual void ThrowOnErrors(XmlTraverser source)
         return (trustedSigningKeys, allowedHashAlgorithms);
     }
 
+    private void CallErrorInspector<TData>(
+        Action<ReadErrorInspectorContext<TData>>? errorInspector,
+        TData data,
+        XmlTraverser source)
+    {
+        if (errorInspector != null)
+        {
+            var context = new ReadErrorInspectorContext<TData>()
+            {
+                Data = data,
+                Errors = source.Errors,
+                XmlSource = source.RootNode
+            };
+
+            errorInspector(context);
+        }
+    }
 }
diff --git a/src/Sustainsys.Saml2/Xml/ReadErrorInspectorContext.cs b/src/Sustainsys.Saml2/Xml/ReadErrorInspectorContext.cs
new file mode 100644
index 000000000..59c002a35
--- /dev/null
+++ b/src/Sustainsys.Saml2/Xml/ReadErrorInspectorContext.cs
@@ -0,0 +1,31 @@
+using Microsoft.Extensions.Configuration.Xml;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using System.Xml;
+
+namespace Sustainsys.Saml2.Xml;
+
+/// <summary>
+/// Context for an error inspector.
+/// </summary>
+/// <typeparam name="TData">Type of the data read</typeparam>
+public class ReadErrorInspectorContext<TData>
+{
+    /// <summary>
+    /// The data read
+    /// </summary>
+    public required TData Data { get; set; }
+
+    /// <summary>
+    /// The XML source, if this was a parsing event.
+    /// </summary>
+    public required XmlNode? XmlSource { get; set; }
+
+    /// <summary>
+    /// The errors found
+    /// </summary>
+    public required IList<Error> Errors { get; set; }
+}
diff --git a/src/Sustainsys.Saml2/Xml/XmlTraverser.cs b/src/Sustainsys.Saml2/Xml/XmlTraverser.cs
index 040b40227..0c3e8e056 100644
--- a/src/Sustainsys.Saml2/Xml/XmlTraverser.cs
+++ b/src/Sustainsys.Saml2/Xml/XmlTraverser.cs
@@ -39,6 +39,8 @@ public class XmlTraverser
     /// </summary>
     private bool childrenHandled = true;
 
+    internal XmlNode? RootNode { get; set; }
+
     /// <summary>
     /// The current node being processed.
     /// </summary>
@@ -50,6 +52,7 @@ public class XmlTraverser
     /// <param name="rootNode">Root node for this traverser</param>
     public XmlTraverser(XmlNode rootNode)
     {
+        RootNode = rootNode;
         CurrentNode = rootNode;
         Errors = [];
     }
diff --git a/src/Tests/Sustainsys.Saml2.Tests/Serialization/SamlXmlReaderTests.AuthnRequest.cs b/src/Tests/Sustainsys.Saml2.Tests/Serialization/SamlXmlReaderTests.AuthnRequest.cs
index fb96b1a40..377a2c298 100644
--- a/src/Tests/Sustainsys.Saml2.Tests/Serialization/SamlXmlReaderTests.AuthnRequest.cs
+++ b/src/Tests/Sustainsys.Saml2.Tests/Serialization/SamlXmlReaderTests.AuthnRequest.cs
@@ -76,7 +76,49 @@ public void ReadAuthnRequest_CanReadOptional()
         actual.Should().BeEquivalentTo(expected);
     }
 
-    // TODO: Test with AssertionConsumerServiceIndex - note mutually exclusive to AcsUrl + Binding
+    [Fact]
+    public void ReadAuthnRequest_ErrorCallback()
+    {
+        var source = GetXmlTraverser(nameof(ReadAuthnRequest_Error));
+
+        var subject = new SamlXmlReader();
+
+        bool errorInspectorCalled = false;
+
+        void errorInspector(ReadErrorInspectorContext<AuthnRequest> context)
+        {
+            context.Data.Id.Should().Be("x123");
+
+            var xmlSourceElement = context.XmlSource as XmlElement;
+            xmlSourceElement.Should().NotBeNull();
+            xmlSourceElement!.GetAttribute("ID").Should().Be("x123");
+            context.Errors.Count.Should().Be(1);
+
+            var error = context.Errors.Single();
+            error.Node.Should().BeSameAs(context.XmlSource);
+            error.LocalName.Should().Be("Version");
+            error.Reason.Should().Be(ErrorReason.MissingAttribute);
+            error.Ignore.Should().BeFalse();
+
+            error.Ignore = true;
+
+            errorInspectorCalled = true;
+        }
 
-    // TODO: Test error callback
+        var actual = subject.ReadAuthnRequest(source, errorInspector);
+
+        errorInspectorCalled.Should().BeTrue();
+    }
+
+    [Fact]
+    public void ReadAuthnRequest_Error()
+    {
+        var source = GetXmlTraverser();
+
+        var subject = new SamlXmlReader();
+
+        subject.Invoking(s => s.ReadAuthnRequest(source))
+            .Should().Throw<SamlXmlException>()
+            .WithMessage("*Version*not found*");
+    }
 }
diff --git a/src/Tests/Sustainsys.Saml2.Tests/Serialization/SamlXmlReaderTests/ReadAuthnRequest_Error.xml b/src/Tests/Sustainsys.Saml2.Tests/Serialization/SamlXmlReaderTests/ReadAuthnRequest_Error.xml
new file mode 100644
index 000000000..0b0e0a322
--- /dev/null
+++ b/src/Tests/Sustainsys.Saml2.Tests/Serialization/SamlXmlReaderTests/ReadAuthnRequest_Error.xml
@@ -0,0 +1,2 @@
+<saml:AuthnRequest xmlns:saml="urn:oasis:names:tc:SAML:2.0:protocol"
+				   ID="x123" IssueInstant="2023-11-24T22:44:14Z" />
\ No newline at end of file