52 lines
3.8 KiB
Markdown
52 lines
3.8 KiB
Markdown
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---
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title: "Certbot DNS-01 hook for Namecheap"
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summary: "A manual auth hook for Certbot, implementing the DNS-01 challenge with Namecheap as the provider. Written in Python."
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date: "2019-10-30"
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tags: ["namecheap", "certbot", "dns-01", "python", "letsencrypt"]
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cover: "/images/namecheap.jpg"
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---
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## The problem
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I want to obtain Let's Encrypt certificates with wildcard subdomains, but to do so, one must prove that they own the entire domain and not just a particular subdomain. This means that the standard HTTP challenges are not enough.
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I was tired of manually doing DNS-01 challenges through Namecheap's dashboard, which involved a laborious process of logging in, navigating to the domain I wanted to obtain certificates for, copying and pasting a special challenge code into a TXT record, waiting for the change to propagate, and repeating this for every single domain I owned, every three months.
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## The research
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Certbot plugins are available for some DNS providers, but Namecheap is not one of those. I was faced with two options: one, move to a different supported provider and transfer all of my domains. Or, two: write a script that could run as a validation hook and thus automate the whole thing.
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> Certbot allows for the specification of pre and post validation hooks when run in manual mode. The flags to specify these scripts are --manual-auth-hook and --manual-cleanup-hook respectively and can be used as follows [...]
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> This will run the authenticator.sh script, attempt the validation, and then run the cleanup.sh script. Additionally certbot will pass relevant environment variables to these scripts [...]
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>
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> -- https://certbot.eff.org/docs/using.html#pre-and-post-validation-hooks
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Namecheap also [provides an API](https://www.namecheap.com/support/api/intro/) to anyone who has spent at least $50 within the last 2 years, [among other alternative requirements](https://www.namecheap.com/support/knowledgebase/article.aspx/9739/63/api--faq/#c).
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## The solution
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I wrote the manual auth hook found here: https://github.com/trwnh/namecheap
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The hook I wrote uses Python, Requests, and BeautifulSoup. Since I just wanted the hook to work, I didn't bother over-engineering this -- this script has some limitations:
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- Namecheap's API uses SLD and TLD instead of a singular domain variable. My script uses an extremely naive approach and simply splits the domain at the dot. I think this might not matter, but I haven't tested further because I don't own any domains with multipart TLDs.
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- None of the API calls are paginated. This means the script only works on accounts with up to 20 domains. I own less than 20 domains, so this is not an issue for me. Also, the methods that require pagination are currently unused in the main function.
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- No error checking or handling was implemented. Theoretically, the script could fail if the domain is expired or locked, but I trust myself to keep all my domains valid and registered.
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- API username, key, etc. are hardcoded instead of being read from some external file. This script was written for my personal use, so I didn't bother going further.
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### Logic
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The pseudocode for this script is as follows:
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1. Get CERTBOT_DOMAIN from Certbot.
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2. Get the host records for this domain.
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3. Get the CERTBOT_VALIDATION code.
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4. Create a TXT host record using this challenge code.
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5. Add this host record to the existing host records.
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6. Upload the host records back to Namecheap.
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The source code can be examined at https://github.com/trwnh/namecheap/blob/master/auth -- I made sure to leave docstrings and use clear function names, so hopefully this is good, readable code.
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## The result
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It works! Now, I can automate my certificate renewals instead of doing it all manually every three months. Maybe one day, I'll even write a cleanup script to delete the TXT challenge records... :)
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