Dynamic Secrets in Github Workflows

dynamic-secret-names.yaml

name: Build
on:
  push:
    branches:
      - main

jobs:
  prepare:
    runs-on: ubuntu-latest
    steps:

      - name: Get branch name
        id: branch
        run: |
          if [[ "${GITHUB_EVENT_NAME}" == "push" ]]; then
             echo "::set-output name=BRANCH_NAME::$(echo ${GITHUB_REF##*/})"
          elif [[ "${GITHUB_EVENT_NAME}" == "repository_dispatch" ]]; then
              echo "::set-output name=BRANCH_NAME::${{ github.event.client_payload.ref }}"
          else
              echo "::set-output name=BRANCH_NAME::INVALID_EVENT_BRANCH_UNKNOWN"
          fi

      - name: Output branch name
        run: echo ${{ steps.branch.outputs.BRANCH_NAME }}

      - name: SET API_SECRET_NAME
        id: api
        run: |
          echo "::set-output name=API_SECRET_NAME::API_${{ steps.branch.outputs.BRANCH_NAME }}";

    outputs:
      BRANCH_NAME: ${{ steps.branch.outputs.BRANCH_NAME }}
      API_SECRET_NAME: ${{ steps.api.outputs.API_SECRET_NAME }}

  build:
    needs: [ prepare ]
    runs-on: ubuntu-latest
    env:
      BRANCH_NAME: ${{ needs.prepare.outputs.BRANCH_NAME }}
      API_SECRET_NAME: ${{ needs.prepare.outputs.API_SECRET_NAME }}
    steps:

      - uses: actions/checkout@v2
        with:
          ref: ${{ github.event.client_payload.ref }}

      - name: Build docker image
        run: |
          docker build  --build-arg=API_URL="${{ secrets[env.API_SECRET_NAME] }}" \
                        -t user/project:${{env.BRANCH_NAME}}-${{ github.sha }} \
                        .