AWS AWS4Signer HttpClientHandler implementation with GraphQL client example

AWS4SignerMessageHandler.cs

static async Task Main(string[] args)
{
    var options = new GraphQLHttpClientOptions
    {
        EndPoint = new Uri("https://countries.trevorblades.com/"),
        HttpMessageHandler = new AWS4SignerMessageHandler(
                                new AmazonAppSyncClient(),
                                "--awsAccessKeyId--",
                                "--awsSecretAccessKey--")
    };
    var graphQLClient = new GraphQLHttpClient(options, new NewtonsoftJsonSerializer());

    var graphQLResponse = await graphQLClient.SendQueryAsync<DataResponse>(new GraphQL.GraphQLRequest(
        @"{
            countries {
                code,
                name
            }
        }"));

    if (graphQLResponse.Errors?.Any() == true)
        throw new Exception(string.Join(Environment.NewLine, graphQLResponse.Errors.Select(e => e.Message)));

    var data = graphQLResponse.Data;

    Console.WriteLine($"Country count: {data.Countries.Count}");
}

public class DataResponse
{
    public List<Country> Countries { get; set; }
}

public class Country
{
    public string Code { get; set; }
    public string Name { get; set; }
}

public class AWS4SignerMessageHandler : HttpClientHandler
{
    private readonly AmazonServiceClient _client;
    private readonly string _awsAccessKeyId;
    private readonly string _awsSecretAccessKey;
    private readonly string _sessionToken;

    public AWS4SignerMessageHandler(AmazonServiceClient client, string awsAccessKeyId, string awsSecretAccessKey, string sessionToken = null)
    {
        _client = client;
        _awsAccessKeyId = awsAccessKeyId;
        _awsSecretAccessKey = awsSecretAccessKey;
        _sessionToken = sessionToken;
    }

    protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        if (_sessionToken != null)
            request.Headers.Add(HeaderKeys.XAmzSecurityTokenHeader, _sessionToken);

        var signingRequest = new AmazonHttpRequestSigning(_client, request)
        {
            Content = await request.Content.ReadAsByteArrayAsync()
        };

        new AWS4Signer().Sign(signingRequest, _client.Config, null, _awsAccessKeyId, _awsSecretAccessKey);

        foreach (var header in signingRequest.Headers)
        {
            if (header.Key != HeaderKeys.HostHeader && header.Key != HeaderKeys.XAmzSecurityTokenHeader && header.Key != HeaderKeys.UserAgentHeader)
                request.Headers.TryAddWithoutValidation(header.Key, header.Value);
        }

        return await base.SendAsync(request, cancellationToken);
    }
}

public class AmazonHttpRequestSigning : IRequest
{
    public AmazonHttpRequestSigning(AmazonServiceClient client, HttpRequestMessage request)
    {
        HttpMethod = request.Method.Method;
        Endpoint = new Uri(request.RequestUri.AbsoluteUri[..request.RequestUri.AbsoluteUri.LastIndexOf(request.RequestUri.AbsolutePath)]);
        ResourcePath = request.RequestUri.AbsolutePath;
        Headers = request.Headers.ToDictionary(e => e.Key, e => e.Value.FirstOrDefault());
        AlternateEndpoint = client.Config.RegionEndpoint;
        AuthenticationRegion = client.Config.AuthenticationRegion;
    }

    public Uri Endpoint { get; set; }
    public string DeterminedSigningRegion { get; set; }
    public RegionEndpoint AlternateEndpoint { get; set; }
    public IDictionary<string, string> Headers { get; }
    public IDictionary<string, string> SubResources { get; }
    public string AuthenticationRegion { get; set; }
    public string HttpMethod { get; set; }
    public string ResourcePath { get; set; }
    public bool UseQueryString { get; set; }
    public bool UseChunkEncoding { get; set; }
    public Stream ContentStream { get; set; }
    public byte[] Content { get; set; }
    public bool? DisablePayloadSigning { get; set; }
    public string OverrideSigningServiceName { get; set; }
    public IDictionary<string, string> PathResources { get; set; }
    public int MarshallerVersion { get; set; }

    #region Not Implemented

    public string RequestName => throw new NotImplementedException();

    public IDictionary<string, string> Parameters => throw new NotImplementedException();

    public ParameterCollection ParameterCollection => throw new NotImplementedException();

    public bool SetContentFromParameters { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
    public long OriginalStreamPosition { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }

    public string ServiceName => throw new NotImplementedException();

    public AmazonWebServiceRequest OriginalRequest => throw new NotImplementedException();

    public string HostPrefix { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
    public bool Suppress404Exceptions { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
    public AWS4SigningResult AWS4SignerResult { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
    public string CanonicalResourcePrefix { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
    public bool UseSigV4 { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }

    public void AddPathResource(string key, string value) => throw new NotImplementedException();
    public void AddSubResource(string subResource) => throw new NotImplementedException();
    public void AddSubResource(string subResource, string value) => throw new NotImplementedException();
    public string ComputeContentStreamHash() => throw new NotImplementedException();
    public string GetHeaderValue(string headerName) => throw new NotImplementedException();
    public bool HasRequestBody() => throw new NotImplementedException();
    public bool IsRequestStreamRewindable() => throw new NotImplementedException();
    public bool MayContainRequestBody() => throw new NotImplementedException();

    #endregion
}

Turns out my gist was a little out of date with the latest libraries. Updated gist to match GraphQL.Client 3.2.0 and AWSSDK.AppSync 3.5.1.23