ASP.NET Core 2.0 Secret Manager

• Download source code from Github

Problem

How do you securely store configuration settings without exposing them to source control in ASP.NET Core.

Solution

Create an empty project and right-click on project solution and click “Manager User Secrets”:

This will open the secrets.json file, add a setting name/value pair:

{
  "SecretSetting":  "SecretValue"
}

Add a POCO for these application settings:

public class AppSettings
    {
        public string SecretSetting { get; set; }
    }

Then, inject configuration settings in the constructor for Startup class:

public static IConfiguration Config { get; private set; }

        public Startup(
            IConfiguration config)
        {
            Config = config;
        }

Then add option services in ConfigureServicees() method of Startup class:

public void ConfigureServices(
            IServiceCollection services)
        {
            services.AddOptions();
            services.Configure<AppSettings>(Config);
        }

Next, inject settings as IOptions<T> interface, where T is your POCO for settings:

public static class UseMiddlewareExtensions
    {
        public static IApplicationBuilder UseHelloWorld(this IApplicationBuilder app)
        {
            return app.UseMiddleware<HelloWorldMiddleware>();
        }
    }

    public class HelloWorldMiddleware
    {
        private readonly RequestDelegate next;
        private readonly AppSettings settings;

        public HelloWorldMiddleware(
            RequestDelegate next,
            IOptions<AppSettings> options)
        {
            this.next = next;
            this.settings = options.Value;
        }

        public async Task Invoke(HttpContext context)
        {
            var jsonSettings = JsonConvert.SerializeObject(this.settings);
            await context.Response.WriteAsync(jsonSettings);
        }
    }

Setup the middle in Configure() method of Startup class:

public void Configure(
            IApplicationBuilder app, 
            IHostingEnvironment env)
        {
            app.UseHelloWorld();
        }

Running the sample application gives you the following output:

Discussion

I discussed in the previous post how configuration settings can be stored in configuration files. However, these files are checked in the source control and not suitable to store confidential settings. In a production environment, these settings can be stored in environment variables or Azure Key Vault however, for development ASP.NET Core provides an alternate solution: Secret Manager.

Secret Manager lets developers store configuration settings in secrets.json file, which isn’t checked-in the source control. The secrets.json file is stored in AppData folder, you could see the exact path by hovering your mouse over the file tab in VS 2017. An important point to note is that the settings are stored in plain text. This file is read by the runtime when loading configuration during building the WebHost, as discussed here.

CLI

You could also use the CLI command dotnet user-secrets to manage the secret settings. In order to do that, first add the following to .csproj:

<ItemGroup>
    <DotNetCliToolReference Include="Microsoft.Extensions.SecretManager.Tools" 
    Version="2.0.0" />
  </ItemGroup>

Now, you could use the following commands to manage the secrets:

Command	Description	Example
list	List all the secrets	dotnet user-secrets list
set	Add/update user secret	dotnet user-secrets set SecretSetting “SecretValue”
remove	Removes a secret	dotnet user-secrets remove SecretSetting
clear	Remove all secrets	dotnet user-secrets clear