Safe storage of app secrets in development in ASP.NET Core

By Rick Anderson, Kirk Larkin, Daniel Roth, and Scott Addie

View or download sample code (how to download)

This document explains how to manage sensitive data for an ASP.NET Core app on a development machine. Never store passwords or other sensitive data in source code. Production secrets shouldn't be used for development or test. Secrets shouldn't be deployed with the app. Instead, production secrets should be accessed through a controlled means like environment variables or Azure Key Vault. You can store and protect Azure test and production secrets with the Azure Key Vault configuration provider.

Environment variables

Environment variables are used to avoid storage of app secrets in code or in local configuration files. Environment variables override configuration values for all previously specified configuration sources.

Consider an ASP.NET Core web app in which Individual User Accounts security is enabled. A default database connection string is included in the project's appsettings.json file with the key DefaultConnection. The default connection string is for LocalDB, which runs in user mode and doesn't require a password. During app deployment, the DefaultConnection key value can be overridden with an environment variable's value. The environment variable may store the complete connection string with sensitive credentials.

Warning

Environment variables are generally stored in plain, unencrypted text. If the machine or process is compromised, environment variables can be accessed by untrusted parties. Additional measures to prevent disclosure of user secrets may be required.

The : separator doesn't work with environment variable hierarchical keys on all platforms. __, the double underscore, is:

  • Supported by all platforms. For example, the : separator is not supported by Bash, but __ is.
  • Automatically replaced by a :

Secret Manager

The Secret Manager tool stores sensitive data during the development of an ASP.NET Core project. In this context, a piece of sensitive data is an app secret. App secrets are stored in a separate location from the project tree. The app secrets are associated with a specific project or shared across several projects. The app secrets aren't checked into source control.

Warning

The Secret Manager tool doesn't encrypt the stored secrets and shouldn't be treated as a trusted store. It's for development purposes only. The keys and values are stored in a JSON configuration file in the user profile directory.

How the Secret Manager tool works

The Secret Manager tool hides implementation details, such as where and how the values are stored. You can use the tool without knowing these implementation details. The values are stored in a JSON file in the local machine's user profile folder:

File system path:

%APPDATA%\Microsoft\UserSecrets\<user_secrets_id>\secrets.json

In the preceding file paths, replace <user_secrets_id> with the UserSecretsId value specified in the project file.

Don't write code that depends on the location or format of data saved with the Secret Manager tool. These implementation details may change. For example, the secret values aren't encrypted, but could be in the future.

Enable secret storage

The Secret Manager tool operates on project-specific configuration settings stored in your user profile.

The Secret Manager tool includes an init command in .NET Core SDK 3.0.100 or later. To use user secrets, run the following command in the project directory:

dotnet user-secrets init

The preceding command adds a UserSecretsId element within a PropertyGroup of the project file. By default, the inner text of UserSecretsId is a GUID. The inner text is arbitrary, but is unique to the project.

<PropertyGroup>
  <TargetFramework>netcoreapp3.1</TargetFramework>
  <UserSecretsId>79a3edd0-2092-40a2-a04d-dcb46d5ca9ed</UserSecretsId>
</PropertyGroup>

In Visual Studio, right-click the project in Solution Explorer, and select Manage User Secrets from the context menu. This gesture adds a UserSecretsId element, populated with a GUID, to the project file.

Set a secret

Define an app secret consisting of a key and its value. The secret is associated with the project's UserSecretsId value. For example, run the following command from the directory in which the project file exists:

dotnet user-secrets set "Movies:ServiceApiKey" "12345"

In the preceding example, the colon denotes that Movies is an object literal with a ServiceApiKey property.

The Secret Manager tool can be used from other directories too. Use the --project option to supply the file system path at which the project file exists. For example:

dotnet user-secrets set "Movies:ServiceApiKey" "12345" --project "C:\apps\WebApp1\src\WebApp1"

JSON structure flattening in Visual Studio

Visual Studio's Manage User Secrets gesture opens a secrets.json file in the text editor. Replace the contents of secrets.json with the key-value pairs to be stored. For example:

{
  "Movies": {
    "ConnectionString": "Server=(localdb)\\mssqllocaldb;Database=Movie-1;Trusted_Connection=True;MultipleActiveResultSets=true",
    "ServiceApiKey": "12345"
  }
}

The JSON structure is flattened after modifications via dotnet user-secrets remove or dotnet user-secrets set. For example, running dotnet user-secrets remove "Movies:ConnectionString" collapses the Movies object literal. The modified file resembles the following JSON:

{
  "Movies:ServiceApiKey": "12345"
}

Set multiple secrets

A batch of secrets can be set by piping JSON to the set command. In the following example, the input.json file's contents are piped to the set command.

Open a command shell, and execute the following command:

type .\input.json | dotnet user-secrets set

Access a secret

To access a secret, complete the following steps:

  1. Register the user secrets configuration source
  2. Read the secret via the Configuration API

Register the user secrets configuration source

The user secrets configuration provider registers the appropriate configuration source with the .NET Configuration API.

The user secrets configuration source is automatically added in Development mode when the project calls CreateDefaultBuilder. CreateDefaultBuilder calls AddUserSecrets when the EnvironmentName is Development:

public static IHostBuilder CreateHostBuilder(string[] args) =>
    Host.CreateDefaultBuilder(args)
        .ConfigureWebHostDefaults(webBuilder =>
        {
            webBuilder.UseStartup<Startup>();
        });

When CreateDefaultBuilder isn't called, add the user secrets configuration source explicitly by calling AddUserSecrets in ConfigureAppConfiguration. Call AddUserSecrets only when the app runs in the Development environment, as shown in the following example:

public class Program
{
    public static void Main(string[] args)
    {
        var host = new HostBuilder()
            .ConfigureAppConfiguration((hostContext, builder) =>
            {
                // Add other providers for JSON, etc.

                if (hostContext.HostingEnvironment.IsDevelopment())
                {
                    builder.AddUserSecrets<Program>();
                }
            })
            .Build();
        
        host.Run();
    }
}

Read the secret via the Configuration API

If the user secrets configuration source is registered, the .NET Configuration API can read the secrets. Constructor injection can be used to gain access to the .NET Configuration API. Consider the following examples of reading the Movies:ServiceApiKey key:

Startup class:

public class Startup
{
    private string _moviesApiKey = null;

    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    public void ConfigureServices(IServiceCollection services)
    {
        _moviesApiKey = Configuration["Movies:ServiceApiKey"];
    }

    public void Configure(IApplicationBuilder app)
    {
        app.Run(async (context) =>
        {
            var result = string.IsNullOrEmpty(_moviesApiKey) ? "Null" : "Not Null";
            await context.Response.WriteAsync($"Secret is {result}");
        });
    }
}

Razor Pages page model:

public class IndexModel : PageModel
{
    private readonly IConfiguration _config;

    public IndexModel(IConfiguration config)
    {
        _config = config;
    }

    public void OnGet()
    {
        var moviesApiKey = _config["Movies:ServiceApiKey"];

        // call Movies service with the API key
    }
}

For more information, see Access configuration in Startup and Access configuration in Razor Pages.

Map secrets to a POCO

Mapping an entire object literal to a POCO (a simple .NET class with properties) is useful for aggregating related properties.

Assume the app's secrets.json file contains the following two secrets:

{
  "Movies:ConnectionString": "Server=(localdb)\\mssqllocaldb;Database=Movie-1;Trusted_Connection=True;MultipleActiveResultSets=true",
  "Movies:ServiceApiKey": "12345"
}

To map the preceding secrets to a POCO, use the .NET Configuration API's object graph binding feature. The following code binds to a custom MovieSettings POCO and accesses the ServiceApiKey property value:

var moviesConfig = 
    Configuration.GetSection("Movies").Get<MovieSettings>();
_moviesApiKey = moviesConfig.ServiceApiKey;

The Movies:ConnectionString and Movies:ServiceApiKey secrets are mapped to the respective properties in MovieSettings:

public class MovieSettings
{
    public string ConnectionString { get; set; }

    public string ServiceApiKey { get; set; }
}

String replacement with secrets

Storing passwords in plain text is insecure. For example, a database connection string stored in appsettings.json may include a password for the specified user:

{
  "ConnectionStrings": {
    "Movies": "Server=(localdb)\\mssqllocaldb;Database=Movie-1;User Id=johndoe;Password=pass123;MultipleActiveResultSets=true"
  }
}

A more secure approach is to store the password as a secret. For example:

dotnet user-secrets set "DbPassword" "pass123"

Remove the Password key-value pair from the connection string in appsettings.json. For example:

{
  "ConnectionStrings": {
    "Movies": "Server=(localdb)\\mssqllocaldb;Database=Movie-1;User Id=johndoe;MultipleActiveResultSets=true"
  }
}

The secret's value can be set on a SqlConnectionStringBuilder object's Password property to complete the connection string:

public class Startup
{
    private string _connection = null;

    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    public void ConfigureServices(IServiceCollection services)
    {
        var builder = new SqlConnectionStringBuilder(
            Configuration.GetConnectionString("Movies"));
        builder.Password = Configuration["DbPassword"];
        _connection = builder.ConnectionString;

        // code omitted for brevity
    }

    public void Configure(IApplicationBuilder app)
    {
        app.Run(async (context) =>
        {
            await context.Response.WriteAsync($"DB Connection: {_connection}");
        });
    }
}

List the secrets

Assume the app's secrets.json file contains the following two secrets:

{
  "Movies:ConnectionString": "Server=(localdb)\\mssqllocaldb;Database=Movie-1;Trusted_Connection=True;MultipleActiveResultSets=true",
  "Movies:ServiceApiKey": "12345"
}

Run the following command from the directory in which the project file exists:

dotnet user-secrets list

The following output appears:

Movies:ConnectionString = Server=(localdb)\mssqllocaldb;Database=Movie-1;Trusted_Connection=True;MultipleActiveResultSets=true
Movies:ServiceApiKey = 12345

In the preceding example, a colon in the key names denotes the object hierarchy within secrets.json.

Remove a single secret

Assume the app's secrets.json file contains the following two secrets:

{
  "Movies:ConnectionString": "Server=(localdb)\\mssqllocaldb;Database=Movie-1;Trusted_Connection=True;MultipleActiveResultSets=true",
  "Movies:ServiceApiKey": "12345"
}

Run the following command from the directory in which the project file exists:

dotnet user-secrets remove "Movies:ConnectionString"

The app's secrets.json file was modified to remove the key-value pair associated with the MoviesConnectionString key:

{
  "Movies": {
    "ServiceApiKey": "12345"
  }
}

dotnet user-secrets list displays the following message:

Movies:ServiceApiKey = 12345

Remove all secrets

Assume the app's secrets.json file contains the following two secrets:

{
  "Movies:ConnectionString": "Server=(localdb)\\mssqllocaldb;Database=Movie-1;Trusted_Connection=True;MultipleActiveResultSets=true",
  "Movies:ServiceApiKey": "12345"
}

Run the following command from the directory in which the project file exists:

dotnet user-secrets clear

All user secrets for the app have been deleted from the secrets.json file:

{}

Running dotnet user-secrets list displays the following message:

No secrets configured for this application.

Additional resources

By Rick Anderson, Daniel Roth, and Scott Addie

View or download sample code (how to download)

This document explains how to manage sensitive data for an ASP.NET Core app on a development machine. Never store passwords or other sensitive data in source code. Production secrets shouldn't be used for development or test. Secrets shouldn't be deployed with the app. Instead, production secrets should be accessed through a controlled means like environment variables or Azure Key Vault. You can store and protect Azure test and production secrets with the Azure Key Vault configuration provider.

Environment variables

Environment variables are used to avoid storage of app secrets in code or in local configuration files. Environment variables override configuration values for all previously specified configuration sources.

Consider an ASP.NET Core web app in which Individual User Accounts security is enabled. A default database connection string is included in the project's appsettings.json file with the key DefaultConnection. The default connection string is for LocalDB, which runs in user mode and doesn't require a password. During app deployment, the DefaultConnection key value can be overridden with an environment variable's value. The environment variable may store the complete connection string with sensitive credentials.

Warning

Environment variables are generally stored in plain, unencrypted text. If the machine or process is compromised, environment variables can be accessed by untrusted parties. Additional measures to prevent disclosure of user secrets may be required.

The : separator doesn't work with environment variable hierarchical keys on all platforms. __, the double underscore, is:

  • Supported by all platforms. For example, the : separator is not supported by Bash, but __ is.
  • Automatically replaced by a :

Secret Manager

The Secret Manager tool stores sensitive data during the development of an ASP.NET Core project. In this context, a piece of sensitive data is an app secret. App secrets are stored in a separate location from the project tree. The app secrets are associated with a specific project or shared across several projects. The app secrets aren't checked into source control.

Warning

The Secret Manager tool doesn't encrypt the stored secrets and shouldn't be treated as a trusted store. It's for development purposes only. The keys and values are stored in a JSON configuration file in the user profile directory.

How the Secret Manager tool works

The Secret Manager tool hides implementation details, such as where and how the values are stored. You can use the tool without knowing these implementation details. The values are stored in a JSON file in the local machine's user profile folder:

File system path:

%APPDATA%\Microsoft\UserSecrets\<user_secrets_id>\secrets.json

In the preceding file paths, replace <user_secrets_id> with the UserSecretsId value specified in the project file.

Don't write code that depends on the location or format of data saved with the Secret Manager tool. These implementation details may change. For example, the secret values aren't encrypted, but could be in the future.

Enable secret storage

The Secret Manager tool operates on project-specific configuration settings stored in your user profile.

To use user secrets, define a UserSecretsId element within a PropertyGroup of the project file. The inner text of UserSecretsId is arbitrary, but is unique to the project. Developers typically generate a GUID for the UserSecretsId.

<PropertyGroup>
  <TargetFramework>netcoreapp2.1</TargetFramework>
  <UserSecretsId>79a3edd0-2092-40a2-a04d-dcb46d5ca9ed</UserSecretsId>
</PropertyGroup>

Tip

In Visual Studio, right-click the project in Solution Explorer, and select Manage User Secrets from the context menu. This gesture adds a UserSecretsId element, populated with a GUID, to the project file.

Set a secret

Define an app secret consisting of a key and its value. The secret is associated with the project's UserSecretsId value. For example, run the following command from the directory in which the project file exists:

dotnet user-secrets set "Movies:ServiceApiKey" "12345"

In the preceding example, the colon denotes that Movies is an object literal with a ServiceApiKey property.

The Secret Manager tool can be used from other directories too. Use the --project option to supply the file system path at which the project file exists. For example:

dotnet user-secrets set "Movies:ServiceApiKey" "12345" --project "C:\apps\WebApp1\src\WebApp1"

JSON structure flattening in Visual Studio

Visual Studio's Manage User Secrets gesture opens a secrets.json file in the text editor. Replace the contents of secrets.json with the key-value pairs to be stored. For example:

{
  "Movies": {
    "ConnectionString": "Server=(localdb)\\mssqllocaldb;Database=Movie-1;Trusted_Connection=True;MultipleActiveResultSets=true",
    "ServiceApiKey": "12345"
  }
}

The JSON structure is flattened after modifications via dotnet user-secrets remove or dotnet user-secrets set. For example, running dotnet user-secrets remove "Movies:ConnectionString" collapses the Movies object literal. The modified file resembles the following JSON:

{
  "Movies:ServiceApiKey": "12345"
}

Set multiple secrets

A batch of secrets can be set by piping JSON to the set command. In the following example, the input.json file's contents are piped to the set command.

Open a command shell, and execute the following command:

type .\input.json | dotnet user-secrets set

Access a secret

The Configuration API provides access to user secrets.

If your project targets .NET Framework, install the Microsoft.Extensions.Configuration.UserSecrets NuGet package.

In ASP.NET Core 2.0 or later, the user secrets configuration source is automatically added in development mode when the project calls CreateDefaultBuilder. CreateDefaultBuilder calls AddUserSecrets when the EnvironmentName is Development:

public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
    WebHost.CreateDefaultBuilder(args)
        .UseStartup<Startup>();

When CreateDefaultBuilder isn't called, add the user secrets configuration source explicitly by calling AddUserSecrets in the Startup constructor. Call AddUserSecrets only when the app runs in the Development environment, as shown in the following example:

public Startup(IHostingEnvironment env)
{
    var builder = new ConfigurationBuilder()
        .SetBasePath(env.ContentRootPath)
        .AddJsonFile("appsettings.json", 
                     optional: false, 
                     reloadOnChange: true)
        .AddEnvironmentVariables();

    if (env.IsDevelopment())
    {
        builder.AddUserSecrets<Startup>();
    }

    Configuration = builder.Build();
}

User secrets can be retrieved via the .NET Configuration API:

public class Startup
{
    private string _moviesApiKey = null;

    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    public void ConfigureServices(IServiceCollection services)
    {
        _moviesApiKey = Configuration["Movies:ServiceApiKey"];
    }

    public void Configure(IApplicationBuilder app)
    {
        app.Run(async (context) =>
        {
            var result = string.IsNullOrEmpty(_moviesApiKey) ? "Null" : "Not Null";
            await context.Response.WriteAsync($"Secret is {result}");
        });
    }
}

Map secrets to a POCO

Mapping an entire object literal to a POCO (a simple .NET class with properties) is useful for aggregating related properties.

Assume the app's secrets.json file contains the following two secrets:

{
  "Movies:ConnectionString": "Server=(localdb)\\mssqllocaldb;Database=Movie-1;Trusted_Connection=True;MultipleActiveResultSets=true",
  "Movies:ServiceApiKey": "12345"
}

To map the preceding secrets to a POCO, use the .NET Configuration API's object graph binding feature. The following code binds to a custom MovieSettings POCO and accesses the ServiceApiKey property value:

var moviesConfig = Configuration.GetSection("Movies")
                                .Get<MovieSettings>();
_moviesApiKey = moviesConfig.ServiceApiKey;

The Movies:ConnectionString and Movies:ServiceApiKey secrets are mapped to the respective properties in MovieSettings:

public class MovieSettings
{
    public string ConnectionString { get; set; }

    public string ServiceApiKey { get; set; }
}

String replacement with secrets

Storing passwords in plain text is insecure. For example, a database connection string stored in appsettings.json may include a password for the specified user:

{
  "ConnectionStrings": {
    "Movies": "Server=(localdb)\\mssqllocaldb;Database=Movie-1;User Id=johndoe;Password=pass123;MultipleActiveResultSets=true"
  }
}

A more secure approach is to store the password as a secret. For example:

dotnet user-secrets set "DbPassword" "pass123"

Remove the Password key-value pair from the connection string in appsettings.json. For example:

{
  "ConnectionStrings": {
    "Movies": "Server=(localdb)\\mssqllocaldb;Database=Movie-1;User Id=johndoe;MultipleActiveResultSets=true"
  }
}

The secret's value can be set on a SqlConnectionStringBuilder object's Password property to complete the connection string:

public class Startup
{
    private string _connection = null;

    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    public void ConfigureServices(IServiceCollection services)
    {
        var builder = new SqlConnectionStringBuilder(
            Configuration.GetConnectionString("Movies"));
        builder.Password = Configuration["DbPassword"];
        _connection = builder.ConnectionString;
    }

    public void Configure(IApplicationBuilder app)
    {
        app.Run(async (context) =>
        {
            await context.Response.WriteAsync($"DB Connection: {_connection}");
        });
    }
}

List the secrets

Assume the app's secrets.json file contains the following two secrets:

{
  "Movies:ConnectionString": "Server=(localdb)\\mssqllocaldb;Database=Movie-1;Trusted_Connection=True;MultipleActiveResultSets=true",
  "Movies:ServiceApiKey": "12345"
}

Run the following command from the directory in which the project file exists:

dotnet user-secrets list

The following output appears:

Movies:ConnectionString = Server=(localdb)\mssqllocaldb;Database=Movie-1;Trusted_Connection=True;MultipleActiveResultSets=true
Movies:ServiceApiKey = 12345

In the preceding example, a colon in the key names denotes the object hierarchy within secrets.json.

Remove a single secret

Assume the app's secrets.json file contains the following two secrets:

{
  "Movies:ConnectionString": "Server=(localdb)\\mssqllocaldb;Database=Movie-1;Trusted_Connection=True;MultipleActiveResultSets=true",
  "Movies:ServiceApiKey": "12345"
}

Run the following command from the directory in which the project file exists:

dotnet user-secrets remove "Movies:ConnectionString"

The app's secrets.json file was modified to remove the key-value pair associated with the MoviesConnectionString key:

{
  "Movies": {
    "ServiceApiKey": "12345"
  }
}

Running dotnet user-secrets list displays the following message:

Movies:ServiceApiKey = 12345

Remove all secrets

Assume the app's secrets.json file contains the following two secrets:

{
  "Movies:ConnectionString": "Server=(localdb)\\mssqllocaldb;Database=Movie-1;Trusted_Connection=True;MultipleActiveResultSets=true",
  "Movies:ServiceApiKey": "12345"
}

Run the following command from the directory in which the project file exists:

dotnet user-secrets clear

All user secrets for the app have been deleted from the secrets.json file:

{}

Running dotnet user-secrets list displays the following message:

No secrets configured for this application.

Additional resources