[View or download sample code](https://github.com/aspnet/Docs/tree/master/aspnetcore/security/app-secrets/samples) ([how to download](xref:index#how-to-download-a-sample))
This document explains techniques for storing and retrieving sensitive data during the development of an ASP.NET Core app. Never store passwords or other sensitive data in source code. Production secrets shouldn't be used for development or test. You can store and protect Azure test and production secrets with the [Azure Key Vault configuration provider](xref:security/key-vault-configuration).
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.
Configure the reading of environment variable values by calling [AddEnvironmentVariables](/dotnet/api/microsoft.extensions.configuration.environmentvariablesextensions.addenvironmentvariables) in the `Startup` constructor:
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 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.
> 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.
The Secret Manager tool abstracts away the 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 configuration file in a system-protected user profile folder on the local machine:
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.
The Secret Manager tool is bundled with the .NET Core CLI in .NET Core SDK 2.1.300 or later. For .NET Core SDK versions before 2.1.300, tool installation is necessary.
> Run `dotnet --version` from a command shell to see the installed .NET Core SDK version number.
A warning is displayed if the .NET Core SDK being used includes the tool:
```console
The tool 'Microsoft.Extensions.SecretManager.Tools' is now included in the .NET Core SDK. Information on resolving this warning is available at (https://aka.ms/dotnetclitools-in-box).
```
Install the [Microsoft.Extensions.SecretManager.Tools](https://www.nuget.org/packages/Microsoft.Extensions.SecretManager.Tools/) NuGet package in your ASP.NET Core project. For example:
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 *.csproj* file. The value of `UserSecretsId` is arbitrary, but is unique to the project. Developers typically generate a GUID for the `UserSecretsId`.
> 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 *.csproj* file. Visual Studio 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:
> 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:
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 *.csproj* file exists:
The Secret Manager tool can be used from other directories too. Use the `--project` option to supply the file system path at which the *.csproj* file exists. For example:
```console
dotnet user-secrets set "Movies:ServiceApiKey" "12345" --project "C:\apps\WebApp1\src\WebApp1"
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.
The [ASP.NET Core Configuration API](xref:fundamentals/configuration/index) provides access to Secret Manager secrets. If your project targets the .NET Framework, install the [Microsoft.Extensions.Configuration.UserSecrets](https://www.nuget.org/packages/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](/dotnet/api/microsoft.aspnetcore.webhost.createdefaultbuilder) to initialize a new instance of the host with preconfigured defaults. `CreateDefaultBuilder` calls [AddUserSecrets](/dotnet/api/microsoft.extensions.configuration.usersecretsconfigurationextensions.addusersecrets) when the [EnvironmentName](/dotnet/api/microsoft.aspnetcore.hosting.ihostingenvironment.environmentname) is [Development](/dotnet/api/microsoft.aspnetcore.hosting.environmentname.development):
When `CreateDefaultBuilder` isn't called during host construction, add the user secrets configuration source with a call to [AddUserSecrets](/dotnet/api/microsoft.extensions.configuration.usersecretsconfigurationextensions.addusersecrets) in the `Startup` constructor:
The [ASP.NET Core Configuration API](xref:fundamentals/configuration/index) provides access to Secret Manager secrets. Install the [Microsoft.Extensions.Configuration.UserSecrets](https://www.nuget.org/packages/Microsoft.Extensions.Configuration.UserSecrets) NuGet package.
Add the user secrets configuration source with a call to [AddUserSecrets](/dotnet/api/microsoft.extensions.configuration.usersecretsconfigurationextensions.addusersecrets) in the `Startup` constructor:
To map the preceding secrets to a POCO, use the `Configuration` API's [object graph binding](xref:fundamentals/configuration/index#bind-to-an-object-graph) feature. The following code binds to a custom `MovieSettings` POCO and accesses the `ServiceApiKey` property value:
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:
The secret's value can be set on a [SqlConnectionStringBuilder](/dotnet/api/system.data.sqlclient.sqlconnectionstringbuilder) object's [Password](/dotnet/api/system.data.sqlclient.sqlconnectionstringbuilder.password) property to complete the connection string:
