'System.Net.Http.HttpRequestException' occurred in mscorlib.dll but was not handled in user code
<p>We are developing the windows forms application to authenticate a windows forms application to a Azure AD.</p>

<p>I have a couple of issues and the resources online are all seems to be outdated.</p>

<p>As suggested by the below link I have created a webapi and native client api  and windows forms application.</p>

<p>In web api I have updated the manifest files as follows</p>

<p>"oauth2Permissions": [</p>

<pre><code>{

  "adminConsentDescription": "Allow the application to access ftpwebapi on behalf of the signed-in user.",

  "adminConsentDisplayName": "Access ftpwebapi",

  "id": "4eebeb18-aee6-408a-bea1-c090766dce23",

  "isEnabled": true,

  "origin": "Application",

  "type": "User",

  "userConsentDescription": "Allow the application to access ftpwebapi on your behalf.",

  "userConsentDisplayName": "Access ftpwebapi",

  "value": "user_impersonation"

}
</code></pre>

<p>],</p>

<p>And added under keys I have added an entry for 2 years and added the webapi to the native client application.</p>

<p>In the windows forms I have added the below code in the button click event.</p>

<p>private async void button1_Click(object sender, EventArgs e)</p>

<pre><code>    {

        string authority = "https://login.windows.net/****";

        string resourceURI = "https://***.com/WebApplication3";

        string clientID = "********-5815-4358-****-*********";

        Uri returnURI = new Uri("http://********.com");

        AuthenticationContext authContext =

            new AuthenticationContext(authority);

        AuthenticationResult authResult =

            authContext.AcquireToken(resourceURI, clientID, returnURI);

        string authHeader = authResult.CreateAuthorizationHeader();

        // don't do this in prod

        System.Net.ServicePointManager.ServerCertificateValidationCallback =

            ((s, c, c2, se) =&gt; true);

        HttpClient client = new HttpClient();

        HttpRequestMessage request =

            new HttpRequestMessage(HttpMethod.Get, "https://localhost:***/task/api/");

        request.Headers.TryAddWithoutValidation("Authorization", authHeader);

        var response = await client.SendAsync(request);

        string responseString = await response.Content.ReadAsStringAsync();

        MessageBox.Show(responseString);
</code></pre>

<p>}</p>

<p>Is it the right way so far ?</p>

<p>And I am agetting an error in</p>

<p>var response = await client.SendAsync(request);</p>

<p>An exception of type 'System.Net.Http.HttpRequestException' occurred in mscorlib.dll but was not handled in user code</p>

<p>Additional information: An error occurred while sending the request.</p>