Lookup a github user using a SAML/SSO linked email address and get the associated github username/login

GraphUserLookup.cs

public class GraphUserLookup
{
    private readonly HttpClient _httpClient;

    public GraphUserLookup(string authToken)
    {
        // TODO - handle tidy up / manage lifetime of this
        _httpClient = new HttpClient();
        _httpClient.BaseAddress = new Uri("https://api.github.com/graphql");
        _httpClient.DefaultRequestHeaders.Add("Authorization", $"Bearer  {authToken}");
        _httpClient.DefaultRequestHeaders.Add("Accept", "application/json");
        _httpClient.DefaultRequestHeaders.Add("User-Agent", "YourUserAgent");
    }

    public async Task<string> GetUserAsync(string login)
    {
        //TODO - Replace yourorgname with the name of your github org    
        var query =
            "query { organization(login: \"yourorgname\") { samlIdentityProvider { externalIdentities(first: 100, userName:\"" +
            login + "\") { edges { node { user { login } samlIdentity { nameId } } } } } } }";

        var result = await PostAsync(query);
        
        var edges = result.Data.Organization.SamlIdentityProvider.ExternalIdentities.Edges.FirstOrDefault();

        var userLogin = edges?.Node.User?.Login;
        
        return userLogin;
    }

    private async Task<GraphQlResponse> PostAsync(string query)
    {
        var request = new HttpRequestMessage();
        request.Method = HttpMethod.Post;

        var payload = new GraphQlQueryPayload
        {
            query = query
        };

        var serialized = JsonConvert.SerializeObject(payload);

        using var stringContent = new StringContent(
            serialized,
            Encoding.UTF8,
            "application/json");
        request.Content = stringContent;
        var response = await _httpClient.SendAsync(request);

        var responsePayload = await response.Content.ReadAsStringAsync();

        return JsonConvert.DeserializeObject<GraphQlResponse>(responsePayload);
    }
}

private class GraphQlQueryPayload
{
    [JsonProperty("query")] 
    public string Query { get; set; }
}

public class GraphQlResponse
{
    [JsonProperty("data")] public Data Data { get; set; }
}

public class Data
{
    [JsonProperty("organization")] public Organization Organization { get; set; }
}

public class Organization
{
    [JsonProperty("samlIdentityProvider")] public SamlIdentityProvider SamlIdentityProvider { get; set; }
}

public class SamlIdentityProvider
{
    [JsonProperty("externalIdentities")] public ExternalIdentities ExternalIdentities { get; set; }
}

public class ExternalIdentities
{
    [JsonProperty("edges")] public Edge[] Edges { get; set; }
}

public class Edge
{
    [JsonProperty("node")] public Node Node { get; set; }
}

public class Node
{
    [JsonProperty("user")] public User User { get; set; }

    [JsonProperty("samlIdentity")] public SamlIdentity SamlIdentity { get; set; }
}

public class SamlIdentity
{
    [JsonProperty("nameId")] public string NameId { get; set; }
}

public class User
{
    [JsonProperty("login")] public string Login { get; set; }
}