.NET StartWebAuthnRegistrationAsync response serialization

[pjk84]

Describe the bug

When i invoke StartWebAuthnRegistrationAsync in the .NET SDK to start the passkey registration procedure i get:

"Cannot Convert DocumentType to List because it is Dictionary"

My implementation is a simple invocation without any parsing or deseralization that would explain this, suggesting it might be an issue in the underlying SDK code.

Regression Issue

• Select this option if this issue appears to be a regression.

Expected Behavior

Method returns StartWebAuthnRegistrationResponse as documented without said serialization issue.

Current Behavior

Invocation throws exception:

Amazon.Runtime.Documents.InvalidDocumentTypeConversionException: Cannot Convert DocumentType to List because it is Dictionary
at Amazon.Runtime.Documents.Document.AssertIsType(DocumentType type)
at Amazon.Runtime.Documents.Document.AsList()
at Amazon.Runtime.Documents.Document.System.Collections.Generic.IEnumerable<Amazon.Runtime.Documents.Document>.GetEnumerator()
at System.Text.Json.Serialization.Converters.IEnumerableDefaultConverter`2.OnWriteResume(Utf8JsonWriter writer, TCollection value, JsonSerializerOptions options, WriteStack& state)
...
at Microsoft.AspNetCore.Mvc.Formatters.SystemTextJsonOutputFormatter.WriteResponseBodyAsync(...)

Reproduction Steps

invoke method StartWebAuthnRegistrationAsync of .NET SDK

Possible Solution

Resolve underlying serialization issue

Additional Information/Context

No response

AWS .NET SDK and/or Package version used

3.7.406.3 but also encountered in latest version

Targeted .NET Platform

net 8.0

Operating System and version

macos 14.3.1 (23D60)

[AlexDaines]

Hi @pjk84, thank you for bringing this to our attention.

I've identified the root cause of the WebAuthn serialization error you've described.

Root Cause: The Document.cs class has an incorrect implementation of IEnumerator<Document> IEnumerable<Document>.GetEnumerator() that always tries to convert the Document to a List even when it contains a Dictionary.

The Issue: When WebAuthn returns response data as a Dictionary structure, the JSON serialization process tries to enumerate it as IEnumerable<Document> but the current implementation calls AsList() which throws the InvalidDocumentTypeConversionException.

Fix: Update the GetEnumerator() method to handle both Dictionary and List types, similar to how the non-generic IEnumerable.GetEnumerator() method already works.

I'm working on a PR with the fix and will update this issue shortly.

[dscpinheiro]

@pjk84 The PR Alex linked was released today (https://github.com/aws/aws-sdk-net/releases/tag/3.7.1060.0). Could you try the latest V3 version of the AWSSDK.CognitoIdentityProvider package?

(We also have an open PR for V4, that'll get merged and released once you confirm the problem is resolved)

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