A somewhat frequent question from developers is how to keep some piece of data secret within an app, such as a secret app key provided by a service.

If this is something that an app acquires at runtime, then you want to use the Credential Locker API to securely store that bit of information. The Credential Locker API is found in the Windows.Security.Credentials.PasswordVault namespace. Whatever is stored here is encrypted, of course, and can only be retrieved by the app that saved it in the first place. What’s also very cool about this feature is that the contents of the Credential Locker is also roamed to the user’s other devices if they have PC Settings > Sync your settings > Password option turned on (and the PC is trusted). So if your app is installed on one device, obtains a secret key for a web service, stores it in the locker, and the user allows those credentials to be roamed, then that secret key will be available to your app when that same user installs it on another device. So you’d want to check for the existence of that secret key even on first run.

If you acquire such a key during app development and include it directly in the app package, then there is the possibility that the key can be discovered and extracted. In this case, the best approach is to store that key in a web service that you query on first run, after which you can save it in the credential locker and retrieve it from there during subsequent sessions.

In other words, assume that everything in your app package is public information and take appropriate steps.

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