Keeping .NET app settings secrets out of source control

Keeping .NET app settings secrets out of source control

Whether your app is a desktop client app or a website, it’s important to keep passwords, connection strings, and API keys out of source control. In .NET, these settings are stored in a app.config or web.config file depending on the type of app you are building and those files would be checked into source control. I’ve done this in the past for many projects. Of course, I never committed production secrets, but it was still a big no-no, but I just never had the time to investigate the proper way to handle this situation…until today.

A quick Google search returned this result: http://www.asp.net/identity/overview/features-api/best-practices-for-deploying-passwords-and-other-sensitive-data-to-aspnet-and-azure. Config files have a simple way of handling this by adding a file attribute to the appSettings section of the web.config file, like so

<appSettings file="secrets.config">
  <add key="testSetting" value="not a secret" />
</appSettings/>

And the secrets.config file looks like this

<appSettings>
  <add key="secretTestSetting" value="very secret" />
  <add key="testSetting" value="I will overwrite" />
</appSettings>

This is the entire file, it is important that the root element is <appSettings> , otherwise you will get a compile or runtime error. Any new keys defined will be added and any existing keys will overwrite the value from the web.config.

Overwriting values in the web.config is very useful for local development. Since the secrets.config file is never checked in, each developer can keep their own local app settings values without worrying about mistakenly checking them in and overriding the web.config default values. No more commenting out values in your web.config!

The same thing works for the connectionStrings section, except in this case the entire section is overwritten. In fact, the web.config can’t have any elements under it or you will get errors. The web.config will look like this

<connectionStrings configSource="connectionStrings.config">
</connectionStrings>

And the connectionStrings.config will look like this

<connectionStrings>
  <clear/>
  <add name="Database" connectionString="very secret" />
</connectionStrings>

As long as your extra files have the .config extension, IIS will never serve them. Also, you should never add these secrets config files to your project to avoid mistakenly deploying them to your servers. Instead, your release process should deploy secrets files separately from code files.

And finally, always add secrets.config and connectionStrings.config to your .gitignore and to get first-time developers setup with secrets, you could include these files somewhere outside of source control, like a file share.

That’s all! Super easy way to keep all your secrets safe in both desktop and web applications. Find the code here: https://github.com/svarcoe/AppSecretsDemoProject

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