Microsoft Graph create class to handle authentication with Azure AD and use access token on subsequent requests.

CS-Graph_Class_MsalAuthenticationProvider.cs

public class MsalAuthenticationProvider : IAuthenticationProvider
{
  private IConfidentialClientApplication _clientApplication;
  private string[] _scopes;

  public MsalAuthenticationProvider(IConfidentialClientApplication clientApplication, string[] scopes) {
    _clientApplication = clientApplication;
    _scopes = scopes;
  }

  public async Task AuthenticateRequestAsync(HttpRequestMessage request)
  {
    var token = await GetTokenAsync();
    request.Headers.Authorization = new AuthenticationHeaderValue("bearer", token);
  }

  public async Task<string> GetTokenAsync()
  {
    AuthenticationResult authResult = null;
    authResult = await _clientApplication.AcquireTokenForClient(_scopes).ExecuteAsync();
    return authResult.AccessToken;
  }
}