Azure LetsEncrypt cannot access .well-known/acme-challenge for my function - azure

Question

I am trying to enable SSL for my azure function using the letsencrypt site-extension for azure as described here. I was following the instructions in that wiki and on this website.
However, I get an error when it tries to verify the website.
The error indicates that the acme-challenge page cannot be accessed (404).
This is my web.config under .well-known/:
<?xml version="1.0" encoding="utf-8"?>
<configuration>
<system.webServer>
<handlers>
<clear />
<add name="ACMEStaticFile" path="*" verb="*" modules="StaticFileModule" resourceType="Either" requireAccess="Read" />
</handlers>
<staticContent>
<remove fileExtension="." />
<mimeMap fileExtension="." mimeType="text/plain" />
</staticContent>
</system.webServer>
<system.web>
<authorization>
<allow users="*"/>
</authorization>
</system.web>
</configuration>
Does anyone have any ideas on what could be going wrong?

Answer 1

Here's how you can do that.
In your function app, create a new proxy for the challenge directory (this is required as the challenge will be a http get to /.well-known/acme-challenge/, and per default a function in a function app will only answer on /api/.
You can setup the proxy in the following way.
proxies.json
{
"$schema": "http://json.schemastore.org/proxies",
"proxies": {
"LetsEncryptProxy": {
"matchCondition": {
"route": "/.well-known/acme-challenge/{code}"
},
"backendUri": "http://%WEBSITE_HOSTNAME%/api/letsencrypt/.well-known/acme-challenge/{code}"
}
}
}
The important setting here is the Route Template: /.well-known/acme-challenge/{*rest} this will match all request that goes to the challenge directory.
Please note that proxies are a preview feature and you have to enable it, for it to work.
Reference:
https://github.com/sjkp/letsencrypt-siteextension/wiki/Azure-Functions-Support
https://blog.bitscry.com/2018/07/06/using-lets-encrypt-ssl-certificates-with-azure-functions/

Answer 2

I figured it out:
Similar to KetanChawda-MSFT's answer, except the proxy needs to hit the api endpoint function that you create.
So here's the function:
// https://YOURWEBSITE.azurewebsites.net/api/letsencrypt/{code}
#r "Newtonsoft.Json"
using System.Net;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Primitives;
using Newtonsoft.Json;
public static async Task<HttpResponseMessage> Run(HttpRequestMessage req, string code, TraceWriter log)
{
log.Info($"C# HTTP trigger function processed a request. {code}");
var content = File.ReadAllText(#"D:\home\site\wwwroot\.well-known\acme-challenge\"+code);
var resp = new HttpResponseMessage(HttpStatusCode.OK);
resp.Content = new StringContent(content, System.Text.Encoding.UTF8, "text/plain");
return resp;
}
And here's the proxy that hits that function when letsEncrypt tries to verify the acme challenge:
{
"$schema": "http://json.schemastore.org/proxies",
"proxies": {
"LetsEncryptProxy": {
"matchCondition": {
"route": "/.well-known/acme-challenge/{code}"
},
"backendUri": "http://%WEBSITE_HOSTNAME%/api/letsencrypt/{code}"
}
}
}