Configure DMARC for Mailgun #22

	name: Preview
	on:
	pull_request_target:
	types: [opened, reopened, synchronize]
	jobs:
	build:
	name: Preview
	runs-on: ubuntu-22.04
	steps:
	- uses: actions/checkout@v4
	# SECURITY: We are checking out dnsconfig.js and creds.json from the PR.
	# These two files cannot perform I/O, and cannot thus be used to leak
	# the secret tokens. As a second layer of security, for this job we use
	# a Cloudflare API token with read-only permissions.
	- name: Checkout config from PR
	run: \|
	git fetch origin +refs/pull/${{ github.event.pull_request.number }}/head
	git checkout FETCH_HEAD -- dnsconfig.js
	- name: Generate preview
	id: preview
	run: \|
	{
	echo "dnscontrol<<DNS_CONTROL_PREVIEW_OUTPUT"
	docker run --rm -v "$(pwd):/dns" --env CLOUDFLARE_ACCOUNT_ID --env CLOUDFLARE_API_TOKEN ghcr.io/stackexchange/dnscontrol:4.18.0 preview \| sed -e 's/\x1b\[[0-9;]*m//g'
	echo "DNS_CONTROL_PREVIEW_OUTPUT"
	} \| tee -a $GITHUB_OUTPUT
	env:
	CLOUDFLARE_ACCOUNT_ID: ${{ secrets.CLOUDFLARE_ACCOUNT_ID }}
	CLOUDFLARE_API_TOKEN: ${{ secrets.CLOUDFLARE_API_TOKEN_READ_ONLY }}
	- name: Create comment
	uses: babel/actions/create-comment@v2
	with:
	token: ${{ secrets.GITHUB_TOKEN }}
	issue: ${{ github.event.pull_request.number }}
	comment: \|
	Preview output:
	```
	${{ steps.preview.outputs.dnscontrol }}
	```

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