Terraform authentication re-uses GitHub Azure Action credentials

terraform-authentication-github-actions.yml

- name: Get Azure CLI
  uses: azure/login@v1
  with:
    creds: ${{ secrets.AZURE_CREDENTIALS }}

- name: Get Terraform
  uses: hashicorp/setup-terraform@v1
  with:
    terraform_version: 'latest'
    terraform_wrapper: false

- name: Prepare environment variables
  env:
    AZURE_CREDENTIALS: ${{ secrets.AZURE_CREDENTIALS }}
  run: | 
    # Parse Azure secret into Terraform variables
    echo "ARM_CLIENT_ID=$( jq -r '.clientId' <<< $AZURE_CREDENTIALS )" >> $GITHUB_ENV;
    echo "ARM_CLIENT_SECRET=$( jq -r '.clientSecret' <<< $AZURE_CREDENTIALS )" >> $GITHUB_ENV;
    echo "ARM_SUBSCRIPTION_ID=$( jq -r '.subscriptionId' <<< $AZURE_CREDENTIALS )" >> $GITHUB_ENV;
    echo "ARM_TENANT_ID=$( jq -r '.tenantId' <<< $AZURE_CREDENTIALS )" >> $GITHUB_ENV
  shell: bash

- name: Terraform Init
  run: terraform init
  shell: bash

Updated for bash. Needs package jq