Monday, July 11, 2016

Can you keep a secret?

A lot of applications store sensitive security related data inside their configuration. Things like API keys, database connection information, even passwords are directly accesible inside the app.config or web.config of a .NET application. Last week a colleague mentioned that they uploaded a project to GitHub accidently exposing the root AWS password for their Amazon account. Whooops!

With ASP.NET Core, Microsoft tries to solve this kind of problems with the introduction of the SecretManager command-line tool. This tool allows you to store these sensitive values in a secure way without exposing them through source control.

If you want to enable it, add the following entry to the “tools” section of project.json:

"Microsoft.Extensions.SecretManager.Tools": {
  "version": "1.0.0-preview1-final",
  "imports": "portable-net45+win8+dnxcore50"

You also need a unique identifier that links your project to the secret manager. Therefore add a userSecretsId for your project in its project.json file:

Now we can use the Secret Manager tool from a command window to set a secret:
dotnet user-secrets set MySecretKey MySecretValue

You can then reference the secret values stored by the secret manager by adding a reference to the Microsoft.Extensions.Configuration.UserSecrets package. Now we can add the “AddUserSecrets()” method to our Startup.cs file:


Probably you only want to do this during development, so wrap it inside an if block:


This will overwrite any configuration options loaded from a configuration file with the contents of the secret store. 

Remark: The secret store actually isn’t too secret, its just a set of JSON files hidden in your user profile folder.  It only prevents you from checking in these values into source control.

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