Can't call microsoft graph api from sharepoint

Question

I create a sharepoint webpart 2019, and want to connect to Microsoft Graph api. However when calling the api i get the following error:

"Could not load file or assembly 'System.Text.Json, Version=5.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51' or one of its dependencies. The system cannot find the file specified."

This is my code:

protected void Page_Load(object sender, EventArgs e)
{
     connectGraph().GetAwaiter().GetResult();
}

private async Task<GraphServiceClient> connectGraph()
{
    try
    {
         string Tenant = "*************************************";
         string ClientId = "*************************************";
         string ClientSecret = "*************************************";
         GraphServiceClient Client;
         PublicClientApplicationBuilder clientApp = PublicClientApplicationBuilder.Create(ClientId);
         IAuthenticationProvider authenticationProvider = new DelegateAuthenticationProvider(async (requestMessage) =>
         {
              if (BearerToken == null || BearerToken.IsExpired())
              {
                   string accessToken = GetUserAccessTokenAsync(clientApp.Build());
              }
              // Append the access token to the request.
              requestMessage.Headers.Authorization = new AuthenticationHeaderValue("bearer", BearerToken.access_token);});
              Client = new GraphServiceClient(authenticationProvider);
              var user = await Client.Users["user@example.com"].Request().GetAsync();
              test.Text = user.DisplayName;
         }
    }
}

private string GetUserAccessTokenAsync(IPublicClientApplication clientApp)
{
    string[] Scopes = { "Directory.AccessAsUser.All" };
    string token = null;
    AuthenticationResult authResult = clientApp.AcquireTokenInteractive(Scopes).ExecuteAsync().Result;
    token = authResult.AccessToken;
    BearerToken = new Token();
    BearerToken.access_token = token;
    return token;
}

public class Token
{
    public string access_token;
    public int expires_in;
    public int expires_on;
    public int not_before;
    public string token_type;
}

The user interface is simple

<asp:TextBox ID="test" runat="server"></asp:TextBox>

I notice my nuget package are blue. Not sure if this is the cause of why I get the error

The errors occurs when i run the

var user = await Client.Users["user@example.com"].Request().GetAsync();

Answer 1

What's the version of your .Net FrameWork? The System.Text.Json NuGet package only supports .NET Framework 4.7.2 and later versions.

You could see the documentation here: https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json-overview?pivots=dotnet-5-0