EWS OAuth .net core 2.1 - oauth

Question

We have a solution today where we use EWS's basic authentication (username and password) with .net Core 2.1, and it works. The problem is that basic authentication will expire in 2020. Therefore, we will transition to the OAuth solution that will work after 2020.
We have tried multiple solutions for this problem, including this: https://learn.microsoft.com/en-us/exchange/client-developer/exchange-web-services/how-to-authenticate-an-ews-application-by-using-oauth, but some of the methods have been updated (AcquireToken -> AcquireTokenAsync).
It's important that the authentication against azure is not client-based, since everything will happen in backend (web api).
Does anyone have a solution to this problem?
This is our current solution:
ExchangeService service = new ExchangeService(ExchangeVersion.Exchange2007_SP1);
service.Credentials = new WebCredentials(<email>, <password>);
service.TraceEnabled = true;
service.TraceFlags = TraceFlags.All;
service.Url = new Uri("https://outlook.office365.com/EWS/Exchange.asmx");
This is an example of what we have tried:
public class Program
{
public static void Run()
{
//tried this as well: string authority = "https://login.windows.net/<devAccountName>.onmicrosoft.com";
string authority = "https://login.microsoftonline.com/<tenantId>/OAuth2/Token";
string clientId = "<clientId>"; // Application ID from Azure
Uri clientAppUri = new Uri("http://localhost:55424/");
Uri resourceHostUri = new Uri("https://outlook.office365.com/EWS/Exchange.asmx");
AuthenticationResult authenticationResult = null;
AuthenticationContext authenticationContext = new AuthenticationContext(authority, false);
string errorMessage = null;
try
{
Console.WriteLine("Trying to acquire token");
PlatformParameters platformParams = new PlatformParameters(PromptBehavior.Auto);
authenticationResult = authenticationContext.AcquireTokenAsync("https://outlook.office365.com/EWS/Exchange.asmx", clientId, clientAppUri, platformParams).Result;
}
catch (AdalException ex)
{
errorMessage = ex.Message;
if (ex.InnerException != null)
{
errorMessage += "\nInnerException : " + ex.InnerException.Message;
}
}
catch (ArgumentException ex)
{
errorMessage = ex.Message;
}
if (!string.IsNullOrEmpty(errorMessage))
{
Console.WriteLine("Failed: {0}" + errorMessage);
return;
}
Console.WriteLine("\nMaking the protocol call\n");
ExchangeService exchangeService = new ExchangeService(ExchangeVersion.Exchange2013);
exchangeService.Url = resourceHostUri;
exchangeService.TraceEnabled = true;
exchangeService.TraceFlags = TraceFlags.All;
exchangeService.Credentials = new OAuthCredentials(authenticationResult.AccessToken);
exchangeService.FindFolders(WellKnownFolderName.Root, new FolderView(10));
}
}
We receive this error message after we log in:
AADSTS50001: The application named
https://outlook.office365.com/EWS/Exchange.asmx was not found in the tenant named <tenantId>. This can happen if the application has not been installed by the administrator of the tenant or consented to by any user in the tenant. You might have sent your authentication request to the wrong tenant.