How do you use Basic Authentication with System.Net.Http.HttpClient?

Question

I'm trying to implement a rest client in c# .net core that needs to first do Basic Authentication, then leverage a Bearer token in subsequent requests.

When I try to do Basic Authentication in combination with client.PostAsync with a FormUrlEncodedContent object, I'm getting an exception:

System.InvalidOperationException occurred in System.Net.Http.dll: 'Misused header name. Make sure request headers are used with HttpRequestMessage, response headers with HttpResponseMessage, and content headers with HttpContent objects.'

//setup reusable http client
HttpClient client = new HttpClient();
Uri baseUri = new Uri(url);
client.BaseAddress = baseUri;
client.DefaultRequestHeaders.Clear();
client.DefaultRequestHeaders.ConnectionClose = true;

//Post body content
var values = new List<KeyValuePair<string,string>>();
values.Add(new KeyValuePair<string, string>("grant_type", "client_credentials"));

var content = new FormUrlEncodedContent(values);

//Basic Authentication
var authenticationString = $"{clientId}:{clientSecret}";
var base64EncodedAuthenticationString = Convert.ToBase64String(System.Text.ASCIIEncoding.ASCII.GetBytes(authenticationString));
content.Headers.Add("Authorization", $"Basic {base64EncodedAuthenticationString}");

//make the request
var task = client.PostAsync("/oauth2/token",content);
var response = task.Result;
response.EnsureSuccessStatusCode();
string responseBody = response.Content.ReadAsStringAsync().Result;
Console.WriteLine(responseBody);

Exception has occurred: CLR/System.InvalidOperationException
An unhandled exception of type 'System.InvalidOperationException' occurred in System.Net.Http.dll: 'Misused header name. Make sure request headers are used with HttpRequestMessage, response headers with HttpResponseMessage, and content headers with HttpContent objects.'
   at System.Net.Http.Headers.HttpHeaders.GetHeaderDescriptor(String name)
   at System.Net.Http.Headers.HttpHeaders.Add(String name, String value)

Answer 1

It looks like you can't use PostAsync and have access to mess with the Headers for authentication. I had to use an HttpRequestMessage and SendAsync.

//setup reusable http client
HttpClient client = new HttpClient();
Uri baseUri = new Uri(url);
client.BaseAddress = baseUri;
client.DefaultRequestHeaders.Clear();
client.DefaultRequestHeaders.ConnectionClose = true;

//Post body content
var values = new List<KeyValuePair<string, string>>();
values.Add(new KeyValuePair<string, string>("grant_type", "client_credentials"));
var content = new FormUrlEncodedContent(values);

var authenticationString = $"{clientId}:{clientSecret}";
var base64EncodedAuthenticationString = Convert.ToBase64String(System.Text.ASCIIEncoding.ASCII.GetBytes(authenticationString));

var requestMessage = new HttpRequestMessage(HttpMethod.Post, "/oauth2/token");
requestMessage.Headers.Authorization = new AuthenticationHeaderValue("Basic", base64EncodedAuthenticationString);
requestMessage.Content = content;

//make the request
var response = await client.SendAsync(requestMessage);
response.EnsureSuccessStatusCode();
string responseBody = await response.Content.ReadAsStringAsync();
Console.WriteLine(responseBody);