add repo-dispatch action with test

.github/actions/repo-dispatch/action.yml

@@ -0,0 +1,46 @@
+name: repository-dispatch
+description: creates repository_dispatch event in target repository
+inputs:
+  secret-token:  # beware: mask is applied below
+    description: fine-grained personal access token with content write permission for the target repo
+    required: true
+    type: string
+  target-repo-owner:
+    description: target repository owner (as in <repo-owner>/<repo-name>)
+    required: true
+    type: string
+  target-repo-name:
+    description: target repository name (as in <repo-owner>/<repo-name>)
+    required: true
+    type: string
+  event-type:
+    # https://docs.github.com/en/webhooks/webhook-events-and-payloads#repository_dispatch
+    description: action in repository_dispatch event (as in github.event.action)
+    required: true
+    type: string
+  client-payload:
+    description: client_payload in repository_dispatch event (a JSON object, as in github.event.client_payload)
+    required: true
+    type: string
+    default: '{}'
+
+runs:
+  using: composite
+  steps:
+    - # https://docs.github.com/en/actions/writing-workflows/choosing-what-your-workflow-does/workflow-commands-for-github-actions#masking-a-value-in-a-log
+      name: mask secret token
+      run: echo "::add-mask::${{ inputs.secret-token }}"
+      shell: bash
+    - name: post to github api dispatches endpoint
+      # https://docs.github.com/en/rest/repos/repos?apiVersion=2022-11-28#create-a-repository-dispatch-event
+      # https://docs.github.com/en/actions/security-for-github-actions/security-guides/automatic-token-authentication
+      run: |
+        curl --location \
+        --fail-with-body \
+        --request POST \
+        --header "Accept: application/vnd.github+json" \
+        --header "Authorization: Bearer ${{ inputs.secret-token }}" \
+        --header "X-GitHub-Api-Version: 2022-11-28" \
+        https://api.github.com/repos/${{ inputs.target-repo-owner }}/${{ inputs.target-repo-name }}/dispatches \
+        --data '{"event_type":"${{ inputs.event-type }}","client_payload":${{ inputs.client-payload }}}'
+      shell: bash

.github/workflows/test-repo-dispatch-listener.yml

@@ -0,0 +1,12 @@
+name: test the receiving end of the repo-dispatch action
+
+on:
+  repository_dispatch:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - run: | 
+          echo "action: ${{ github.event.action }}"
+          echo "payload: ${{ github.event.client_payload.my-key }}"

.github/workflows/test-repo-dispatch.yml

@@ -0,0 +1,25 @@
+# This workflow tests the reusable repo-dispatch action
+
+name: test repo-dispatch action
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+  workflow_dispatch:
+
+jobs:
+  dispatch:
+    runs-on: ubuntu-latest
+    steps:
+      - name: checkout in order to use local action
+        uses: actions/checkout@v4
+      - name: test action
+        uses: ./.github/actions/repo-dispatch
+        with:
+          secret-token: ${{ secrets.personal_access_token }}
+          target-repo-name: ${{ github.event.repository.name }}
+          target-repo-owner: ${{ github.repository_owner }}
+          event-type: my-event
+          client-payload: '{"my-key": "my-value"}'