Document how to use secrets with if: conditionals in GitHub Actions workflows

content/actions/security-guides/encrypted-secrets.md

@@ -227,6 +227,10 @@ steps:
 ```
 {% endraw %}
 
+Secrets cannot be directly referenced in `if:` conditionals. Instead, consider setting secrets as job-level environment variables, then referencing the environment variables to conditionally run steps in the job. For more information, see "[Context availability](/actions/learn-github-actions/contexts#context-availability)" and [`jobs.<job_id>.steps[*].if`](/actions/using-workflows/workflow-syntax-for-github-actions#jobsjob_idstepsif).
+
+If a secret has not been set, the return value of an expression referencing the secret (such as {% raw %}`${{ secrets.SuperSecret }}`{% endraw %} in the example) will be an empty string.
+
 Avoid passing secrets between processes from the command line, whenever possible. Command-line processes may be visible to other users (using the `ps` command) or captured by [security audit events](https://docs.microsoft.com/windows-server/identity/ad-ds/manage/component-updates/command-line-process-auditing). To help protect secrets, consider using environment variables, `STDIN`, or other mechanisms supported by the target process.
 
 If you must pass secrets within a command line, then enclose them within the proper quoting rules. Secrets often contain special characters that may unintentionally affect your shell. To escape these special characters, use quoting with your environment variables. For example:

content/actions/using-workflows/workflow-syntax-for-github-actions.md

@@ -342,6 +342,31 @@ steps:
     uses: actions/[email protected]
 ```
 
+### Example: Using secrets
+
+Secrets cannot be directly referenced in `if:` conditionals. Instead, consider setting secrets as job-level environment variables, then referencing the environment variables to conditionally run steps in the job.
+
+If a secret has not been set, the return value of an expression referencing the secret (such as {% raw %}`${{ secrets.SuperSecret }}`{% endraw %} in the example) will be an empty string.
+
+{% raw %}
+```yaml
+name: Run a step if a secret has been set
+on: push
+jobs:
+  my-jobname:
+    runs-on: ubuntu-latest
+    env:
+      super_secret: ${{ secrets.SuperSecret }}
+    steps:
+      - if: ${{ env.super_secret != '' }}
+        run: echo 'This step will only run if the secret has a value set.'
+      - if: ${{ env.super_secret == '' }}
+        run: echo 'This step will only run if the secret does not have a value set.'
+```
+{% endraw %}
+
+For more information, see "[Context availability](/actions/learn-github-actions/contexts#context-availability)" and "[Encrypted secrets](/actions/security-guides/encrypted-secrets)."
+
 ### `jobs.<job_id>.steps[*].name`
 
 A name for your step to display on {% data variables.product.prodname_dotcom %}.