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Trigger STO scans to block pull requests with vulnerabilities

You can create Git event triggers to support a variety of STO workflows and use cases. This topic describes how to do the following:

  • Trigger an STO pipeline that detects vulnerabilities and blocks merging when a pull request targets a protected branch and/or updates specific files in the repo.
  • Include a keyword in a review comment to trigger a new scan if a previous pipeline execution failed.
  • Set branch protection rules that block pull requests if the STO pipeline fails.

The following steps outline the basic workflow:

  1. Create a trigger for your Harness pipeline.

    This should automatically register an outbound webhook in your Git repo.

  2. Create a pull request to test the webhook and trigger.

  3. Add a branch protection rule to ensure that the pull request cannot be merged if the Harness pipeline fails.

Before you begin​

These workflows require the following:

  • A connector to your Git service.
  • A Harness pipeline with an STO repository scan step, for example, Bandit or Semgrep.
  • The Codebase in your pipeline should point to the Git repo that you want to scan.

Create the trigger (Harness)​

The following sections describe two triggers that can be very useful in the context of STO scanning:

Trigger on a changed file​

You can specify a trigger that says: If a pull request updates any of these files, run the pipeline and scan the repo.

This type of trigger supports uses cases such as:

  • If the pull request updates any file that matches the trigger filter, run a SAST scan and block the PR if the scan results meet the Fail on Severity threshold.

  • If the pull request updates a specific file of interest, such as a pom.xml workspace file, run an SCA scan and block the PR if the scan results meet the Fail on Severity threshold.

Trigger setup​

  1. Go to your STO pipeline, select Triggers (top right), and add a new trigger.

  2. Set up the trigger as follows.

Configuration​

  1. Connector to your Git service.

  2. Repository name.

  3. Event = Pull Request.

  4. Actions to trigger the pipeline

Condition​

The following conditions are the most relevant to this workflow. You can add other conditions as needed. Triggers are complex filters in which all conditions are AND-ed together.

  1. Target Branch This should match your target baseline, such as main.

  2. Changed Files The files that trigger the STO pipeline if they have updates in the PR. You can specify multiple files using the operators In, Not In, and Regex.

Here's a simple example: trigger a build if a PR seeks to update a specific pom.xml in the main branch.

Pipeline input​

The pipeline input should be preconfigured correctly, with Build Type set to Git Pull Request.

Test the trigger​

After you create the trigger, proceed to Test the outbound webhook and trigger.

YAML trigger example

trigger:
  name: sast-test-trigger
  identifier: sasttesttrigger
  enabled: true
  encryptedWebhookSecretIdentifier: ""
  description: ""
  tags: {}
  orgIdentifier: default
  stagesToExecute: []
  projectIdentifier: default
  pipelineIdentifier: triggertestupdatepom
  source:
    type: Webhook
    spec:
      type: Github
      spec:
        type: PullRequest
        spec:
          connectorRef: my_github_connector
          autoAbortPreviousExecutions: false
          payloadConditions:
            - key: changedFiles
              operator: Equals
              value: /full/path/to/pom.xml
            - key: targetBranch
              operator: Equals
              value: main
          headerConditions: []
          repoName: dvpwa-djb
          actions:
            - Open
            - Reopen
  inputYaml: |
      pipeline:
         identifier: triggertestupdatepom
         properties:
           ci:
             codebase:
               build:
                 type: PR
                 spec:
                   number: <+trigger.prNumber>


Trigger on a PR review comment​

You can specify a trigger that says: If a reviewer includes a specific keyword in a pull-request review comment, run the pipeline and scan the repo.

This type of trigger is useful when a pipeline execution fails for reasons other than Fail on Severity. If the STO scan doesn't finish in the original execution, a reviewer can add a review comment with a keyword such as RERUN_STO_PIPELINE.

Trigger setup​

  1. Go to your STO pipeline, select Triggers (top right), and add a new trigger.

  2. Set up the trigger as follows.

Configuration​

  1. Connector to your Git service.

  2. Repository name.

  3. Event = Issue Comment.

  4. Actions, such as Create and Edit, to trigger the scan. You can also select All actions to allow reviewers to trigger a scan at any time.

Condition​

The following conditions are the most relevant to this workflow. You can add other conditions as needed. Triggers are complex filters in which all conditions are AND-ed together.

  1. Target Branch This should match your target baseline.

  2. Enter the following JEXL condition with the keyword to trigger a new scan:

    <+trigger.payload.comment.body>.contains("RERUN_STO_SCAN")

Pipeline input​

The pipeline input should be preconfigured correctly, with Build Type should be set to Git Pull Request.

Test the trigger​

After you create the trigger, proceed to Test the outbound webhook and trigger.

YAML trigger example

trigger:
  name: dvpwa-issue-comment-KEYWORD
  identifier: dvpwaissuecommentKEYWORD
  enabled: false
  encryptedWebhookSecretIdentifier: ""
  description: ""
  tags: {}
  orgIdentifier: default
  stagesToExecute: []
  projectIdentifier: sto_tutorials
  pipelineIdentifier: prtest
  source:
    type: Webhook
    spec:
      type: Github
      spec:
        type: IssueComment
        spec:
          connectorRef: my_github_connector
          autoAbortPreviousExecutions: false
          payloadConditions:
            - key: targetBranch
              operator: In
              value: master, develop
          headerConditions: []
          jexlCondition: <+trigger.payload.comment.body>.contains("RERUN_STO_SCAN")
          repoName: dvpwa
          actions: []
  inputYaml: |
    pipeline:
      identifier: prtest
      properties:
        ci:
          codebase:
            build:
              type: PR
              spec:
                number: <+trigger.prNumber>


Test the outbound webhook and trigger​

Verify the webhook (Git)​

Once you add a trigger to your pipeline, your Git service provider should create a webhook for the trigger automatically. This is true for all non-custom webhooks and all Git providers supported by Harness.

  1. Go to your repo in your SCM provider, navigate to the repo's webhook settings, and verify that the webhook got registered. In GitHub, for example, go to Settings > Webhooks.

  2. If you don't see a webhook, you can add one manually.

For more information, go to Register the webhook in the Git provider.

Test the webhook and trigger​

To test your trigger, update your Git repo to verify that the trigger works as intended.

  • To verify the changed-file trigger described above:

    • Go to the root branch you specified in the trigger.
    • Update the file you specified in the trigger. Then create a pull request in a new branch.

  • To verify the review-comment trigger described above, create a pull request and then add a review comment with the keyword you specified.

    • Go to the root branch you specified in the trigger.
    • Create a pull request in a new branch.
    • Add a review comment with the keyword you specified in the trigger.

You should now see the following:

  1. In the Git repo, the request and response were successful.

  2. In the Pipeline Executions page of your Harness pipeline, the trigger starts a new execution.

  3. In the Git pull request, the pipeline execution appears as an automated check.

If the trigger doesn't work as intended, go to Troubleshoot Git event triggers.

Add a branch protection rule for the Git repo​

The final step is to ensure that a PR cannot be merged if the STO pipeline fails. To do this, you create a protection rule for your root branch.

The following steps describe a simple setup in GitHub. For more information, go to Managing a branch protection rule in the GitHub documentation.

If you're using a different SCM, go to the SCM documentation and search for branch protection.

Add the protection rule​

  1. Go to your Git repo and select Settings > Branches > Add Rule.

  2. In Branch name pattern, add a string or regular expression for the branch or branches you want to protect. This should match your target baseline.

  3. Select Require a pull request before merging and Require Approvals. This isn't required, but it's good practice.

  4. Select Require status checks to pass before merging.

  5. In the search field below, enter the first characters of the check name and then select the check.

  6. Configure any other settings as appropriate.

  7. Scroll to the bottom of the page and save your rule.

Test the protection rule​

Now that you've set up the rule, trigger another pipeline execution to verify that the rule stops the pull request.

note

To verify the branch protection rule, you must ensure that your STO pipeline fails. To configure your pipeline to fail temporarily, you can do one of the following:

  • Set Fail on Severity to Low in the scan step of your pipeline. Then scan a repo with known vulnerabilities.
  • Add a temporary Run step to your pipeline with the command exit(1).

  1. Trigger another pipeline execution.

  2. Now, merging is blocked if the Harness pipeline fails.

For more information​