Creating Self Signed Certificate

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When using self-signed certificates, there are different ways to create and use them for development and testing scenarios. In this guide, you'll cover using self-signed certificates with dotnet dev-certs, and other options like PowerShell and OpenSSL.

You can then validate that the certificate will load using an example such as an ASP.NET Core app hosted in a container.

Prerequisites

In the sample, you can utilize either .NET Core 3.1 or .NET 5.

For dotnet dev-certs, be sure to have the appropriate version of .NET installed:

This sample requires Docker 17.06 or later of the Docker client.

Prepare sample app

You'll need to prepare the sample app depending on which runtime you'd like to use for testing, either .NET Core 3.1 or .NET 5.

Creating self signed certificate powershell

For this guide, you'll use a sample app and make changes where appropriate.

.NET Core 3.1 sample app

Get the sample app.

Navigate to the repository locally and open up the workspace in an editor.

Note

If you're looking to use dotnet publish parameters to trim the deployment, you should make sure that the appropriate dependencies are included for supporting SSL certificates.Update the dotnet-dockersamplesaspnetappaspnetapp.csproj to ensure that the appropriate assemblies are included in the container. For reference, check how to update the .csproj file to support ssl certificates when using trimming for self-contained deployments.

Make sure the aspnetapp.csproj includes the appropriate target framework:

Modify the Dockerfile to make sure the runtime points to .NET Core 3.1:

Make sure you're pointing to the sample app.

Build the container for testing locally.

.NET 5 sample app

For this guide, the sample aspnetapp should be checked for .NET 5.

Check sample app Dockerfile is using .NET 5.

Depending on the host OS, the ASP.NET runtime may need to be updated. For example, changing from mcr.microsoft.com/dotnet/aspnet:5.0-nanoservercore-2009 AS runtime to mcr.microsoft.com/dotnet/aspnet:5.0-windowsservercore-ltsc2019 AS runtime in the Dockerfile will help with targeting the appropriate Windows runtime.

For example, this will help with testing the certificates on Windows:

If we're testing the certificates on Linux, you can use the existing Dockerfile.

Make sure the aspnetapp.csproj includes the appropriate target framework:

Note

If you want to use dotnet publish parameters to trim the deployment, make sure that the appropriate dependencies are included for supporting SSL certificates.Update the dotnet-dockersamplesaspnetappaspnetapp.csproj to ensure that the appropriate assemblies are included in the container. For reference, check how to update the .csproj file to support ssl certificates when using trimming for self-contained deployments.

Make sure you're pointing to the sample app.

Build the container for testing locally.

Create a self-signed certificate

You can create a self-signed certificate:

With dotnet dev-certs

You can use dotnet dev-certs to work with self-signed certificates. This example uses a PowerShell console.

Note

The certificate name, in this case aspnetapp.pfx must match the project assembly name. crypticpassword is used as a stand-in for a password of your own choosing. If console returns 'A valid HTTPS certificate is already present.', a trusted certificate already exists in your store. It can be exported using MMC Console.

Configure application secrets, for the certificate:

Note

Note: The password must match the password used for the certificate.

Run the container image with ASP.NET Core configured for HTTPS:

Creating Self Signed Certificate Error

Once the application starts, navigate to https://localhost:8001 in your web browser.

Clean up

If the secrets and certificates are not in use, be sure to clean them up.

With PowerShell

You can use PowerShell to generate self-signed certificates. The PKI Client can be used to generate a self-signed certificate.

The certificate will be generated, but for the purposes of testing, should be placed in a cert store for testing in a browser.

At this point, the certificates should be viewable from an MMC snap-in.

You can run the sample container in Windows Subsystem for Linux (WSL):

Note

Note that with the volume mount the file path could be handled differently based on host. For example, in WSL we may replace /c/certs with /mnt/c/certs.

If you're using the container built earlier for Windows, the run command would look like the following:

Once the application is up, navigate to contoso.com:8001 in a browser.

Be sure that the host entries are updated for contoso.com to answer on the appropriate ip address (for example 127.0.0.1). If the certificate isn't recognized, make sure that the certificate that is loaded with the container is also trusted on the host, and that there's appropriate SAN / DNS entries for contoso.com.

Clean up

With OpenSSL

You can use OpenSSL to create self-signed certificates. This example will use WSL / Ubuntu and a bash shell with OpenSSL.

This will generate a .crt and a .key.

To get a .pfx, use the following command:

Note

The .aspnetcore 3.1 example will use .pfx and a password. Starting with the .net 5 runtime, Kestrel can also take .crt and PEM-encoded .key files.

Depending on the host os, the certificate will need to be trusted. On a Linux host, 'trusting' the certificate is different and distro dependent.

For the purposes of this guide, here's an example in Windows using PowerShell:

For .NET Core 3.1, run the following command in WSL:

Starting with .NET 5, Kestrel can take the .crt and PEM-encoded .key files. You can run the sample with the following command for .NET 5:

Note

Note that in WSL, the volume mount path may change depending on the configuration.

Creating

For .NET Core 3.1 in Windows, run the following command in Powershell:

Creating Self Signed Certificate

For .NET 5 in Windows, run the following command in PowerShell:

Once the application is up, navigate to contoso.com:8001 in a browser.

Creating Self Signed Certificate Openssl

Be sure that the host entries are updated for contoso.com to answer on the appropriate ip address (for example 127.0.0.1). If the certificate isn't recognized, make sure that the certificate that is loaded with the container is also trusted on the host, and that there's appropriate SAN / DNS entries for contoso.com.

Creating Self Signed Certificate Windows

Clean up

Creating Self Signed Certificate

Be sure to clean up the self-signed certificates once done testing.