ASPNET Core websites, developping with SSL

While working on the backend for To-Do.Studio, we ran into a scenario where we needed to test on a developer’s machine with https (ssl) enabled.

note – we use Kestral for testing and not IISExpress.

First thing we did was to try and add a https url in the LaunchSettings.json file. That didn’t work 🙂

What we found was that had to configure Kestral manually and tell it which certificate to use. The code in our Program class looks like this :

public static IWebHost BuildWebHost(string[] args) =>
     .UseKestrel(t => {
        t.Listen(IPAddress.Loopback, 55172);
        t.Listen(IPAddress.Loopback, 55000, o =>
            o.UseHttps("localhostCertificate.pfx", "password");

But how do we get a certificate ? There are various ways but i didn’t feel like finding my win32 sdk as some instruction’s on the web… so i decided to use my Ubuntu WSL…

Two commands

erik@ErikLAPTOP:~$ openssl req -x509 -days 10000 -newkey rsa:2048 -keyout cert.pem -out cert.pem
erik@ErikLAPTOP:~$openssl pkcs12 -export -in cert.pem -inkey cert.pem -out cert.pfx

and i had a good looking self made certificate. The hardest part was to copy this cert.pfx file to a Windows directory so i could use it my code.

Voilà ! after modifying my LaunchSettings.json, i could test in either http or https mode !

"ToDoStudio.Server_http": {
 "commandName": "Project",
 "launchBrowser": true,
 "environmentVariables": {
 "applicationUrl": "http://localhost:55172/"
 "ToDoStudio.Server_https": {
 "commandName": "Project",
 "launchBrowser": true,
 "environmentVariables": {
 "applicationUrl": "https://localhost:55000/"

Kestral? Do you mean “Kestrel”?

Yep! sorry for the typo!