JSON Patch secrets into appsettings.json

Another useful feature in the ServiceStack x dotnet tool I wanted to highlight is its built-in support for JSON Patching. This feature provides you with a robust mechanism for modifying your JSON files, providing a precise and granular way to manage configurations, that's especially useful when automating changes from a continuous integration environment.

What is JSON Patching?​

JSON Patch, as specified in RFC 6902, is a format for expressing a sequence of operations to apply to a JSON document. It allows us to add, remove, replace, copy, move and test elements within the JSON structure, making it a versatile tool in managing and altering configurations.

Here's a quick overview of the supported operations:

The x dotnet tool implements these operations, making it a handy utility for managing your JSON configurations.

An Example with SMTP Settings​

Let's dive into a practical example. We'll be working with an appsettings.json file, a common sight in .NET projects, which often houses sensitive settings like SMTP config. Suppose we have the following structure with an empty smtp object:

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning"
    }
  },
  "smtp": {}
}

We need to fill this smtp object with settings such as username, password, host, port, and more. To automate filling these values, we can use the ServiceStack x tool to apply a json.patch.

The json.patch file to accomplish this would look something like:

[
  {
    "op": "add",
    "path": "/smtp",
    "value": {
      "UserName": "AWS_ACCESS_KEY_ID",
      "Password": "AWS_SECRET_ACCESS_KEY",
      "Host": "email-smtp.us-east-1.amazonaws.com",
      "Port": 587,
      "From": "email address",
      "FromName": "From Name",
      "Bcc": "bcc email address"
    }
  }
]

Once this patch is applied, our appsettings.json transforms into:

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning"
    }
  },
  "smtp": {
    "UserName": "AWS_ACCESS_KEY_ID",
    "Password": "AWS_SECRET_ACCESS_KEY",
    "Host": "email-smtp.us-east-1.amazonaws.com",
    "Port": 587,
    "From": "email address",
    "FromName": "From Name",
    "Bcc": "bcc email address"
  }
}

You can apply this patch using the x tool's patch command:

x patch appsettings.json.patch

This expects both the appsettings.json.patch and appsettings.json files to be local. Optionally, you can specify both files if their names differ.

x patch changes.json.patch appsettings.json

Using in CI Environments​

Another significant benefit of this feature is the convenience it provides in CI environments, such as GitHub Actions. Secrets and other environment-specific configurations often need to be injected during the CI process. This is where JSON patching can be extremely useful.

Consider the following step in a GitHub Actions workflow:

- name: Apply SMTP Settings
  working-directory: ./MyApp
  run: | 
    cat <<EOF >> appsettings.json.patch
    ${‎{ secrets.APPSETTINGS_PATCH}‎}
    EOF
    x patch appsettings.json.patch

Here, the SMTP settings are stored securely as GitHub secrets as JSON patch syntax, and then added to the appsettings.json file during the CI process using the x tool. This ensures that sensitive data like your SMTP password remains secure and is not hardcoded into your app's source code.

Wrapping Up​

The ability to use JSON Patch files to manipulate JSON data adds a powerful tool to your .NET developer toolkit. Whether you're managing complex configurations or securing sensitive data in CI processes, ServiceStack's x dotnet tool and its JSON Patching feature gives you an easier way to automate changes to JSON files.