private async Task SharedKeyAuthentication()

in src/Microsoft.Atlas.CommandLine/OAuth2/HttpClientFactory.cs [85:139]
48 lines of code
3 McCabe index (conditional complexity)

        private async Task<HttpResponseMessage> SharedKeyAuthentication(HttpRequestMessage request, CancellationToken cancellationToken, Func<HttpRequestMessage, CancellationToken, Task<HttpResponseMessage>> next)
        {
            var authorization = request.Headers.Authorization;
            if (authorization != null && string.Equals(authorization.Scheme, "SharedKey"))
            {
                var parts = authorization.Parameter.Split(":", 2);
                var account = parts[0];
                var key = Convert.FromBase64String(parts[1]);

                var canonicalizedHeaders = request.Headers
                    .Where(header => header.Key.StartsWith("x-ms-"))
                    .Select(header => Tuple.Create(header.Key.ToLowerInvariant(), string.Join(",", header.Value)))
                    .OrderBy(header => header.Item1, StringComparer.InvariantCulture)
                    .Select(header => $"{header.Item1}:{header.Item2}\n")
                    .Aggregate(string.Empty, (a, b) => a + b);

                var queryParameters = QueryHelpers
                    .ParseNullableQuery(request.RequestUri.Query)
                    ?.Select((System.Collections.Generic.KeyValuePair<string, Extensions.Primitives.StringValues> item) =>
                    {
                        var name = UrlEncoder.Default.Encode(item.Key.ToLower());
                        var value = string.Join(",", item.Value.Select(UrlEncoder.Default.Encode));
                        return new { name, value };
                    })
                    ?.OrderBy(item => item.name)
                    ?.Select(item => $"\n{item.name}:{item.value}")
                    ?.Aggregate(string.Empty, (a, b) => a + b)
                    ?? string.Empty;

                var canonicalizedResource = $"/{account}{request.RequestUri.AbsolutePath}{queryParameters}";

                var signatureString =
                    $"{request.Method}\n" +
                    $"{request.Content?.Headers?.ContentEncoding}\n" +
                    $"{request.Content?.Headers?.ContentLanguage}\n" +
                    $"{request.Content?.Headers?.ContentLength}\n" +
                    $"{request.Content?.Headers?.ContentMD5}\n" +
                    $"{request.Content?.Headers?.ContentType}\n" +
                    $"{request.Headers.Date}\n" +
                    $"{request.Headers.IfModifiedSince}\n" +
                    $"{request.Headers.IfMatch}\n" +
                    $"{request.Headers.IfNoneMatch}\n" +
                    $"{request.Headers.IfUnmodifiedSince}\n" +
                    $"{request.Headers.Range}\n" +
                    $"{canonicalizedHeaders}" +
                    $"{canonicalizedResource}";

                var hmac = new HMACSHA256(key);
                var signature = hmac.ComputeHash(Encoding.ASCII.GetBytes(signatureString));

                request.Headers.Authorization = new AuthenticationHeaderValue("SharedKey", $"{account}:{Convert.ToBase64String(signature)}");
            }

            return await next(request, cancellationToken);
        }