Posted on by Prince PARK

How to Use Let’s Encrypt on Windows Server with IIS

This guide explains how to enable a FREE SSL certificate using Let’s Encrypt on a Windows Server running IIS. Specifically, it addresses the challenges of using wildcard certificates for multiple websites with different domains and subdomains.

Scenario:

You have a Windows Server 2019 with IIS 10, a single IP address, and multiple HTTPS websites hosted with different domain names. For subdomains under the same primary domain (like *.example.com), a wildcard certificate works perfectly. However, complications arise when adding websites from different domains, such as mydomain.com.

Initial Setup Example:

IIS 10 hosts the following sites:

  • ABC Server (Website)
    • abc.api.example.com – HTTPS @ 443
  • ABC Client (Website)
    • abc.example.com – HTTPS @ 443
    • bcd.example.com – HTTPS @ 443
    • cde.example.com – HTTPS @ 443
    • admin.example.com – HTTPS @ 443
  • XYZ App (Website)
    • xyz.example.com – HTTPS @ 443
  • SEQ (Website)
    • seq.mydomain.com – HTTPS @ 443

Managing these SSL certificates with multiple domain names can be tricky, but Let’s Encrypt simplifies the process.

Steps to Enable Let’s Encrypt SSL on IIS

  • Enable IIS and Create the .well-known Folder
    • Follow this guide to create the .well-known directory for SSL validation
      • Create a folder on the C drive named well-known. Inside, create another folder called pki-validation. Example: C:\well-known\pki-validation.
      • Place the required validation file in the pki-validation folder.
      • Open IIS Manager and for each site, right-click and select Add Virtual Directory.
      • In the Alias field, enter .well-known. In the Physical Path field, enter the path to the folder you created, e.g., C:\well-known\pki-validation.
      • Confirm with OK. The folder and files should now be accessible via the web.
  • Set Proper Permissions for the C:\well-known\pki-validation Folder
    • Follow this IIS 403 Forbidden solution:
      • Right-click the .well-known folder and select Properties.
      • Navigate to the Security tab.
      • Click Edit and ensure IIS_IUSRS is listed. If not, click Add
      • In the Enter the object names box, type IIS_IUSRS and click OK.
      • Set Read & execute, List folder contents, and Read permissions for IIS_IUSRS.
  • Validate DNS Entries for Each Domain/Subdomain
    • Use a tool like Google Dig to validate DNS entries for the following domains:
      • abc.api.example.com
      • abc.example.com
      • bcd.example.com
      • cde.example.com
      • admim.example.com
      • xyz.example.com
      • seq.mydomain.com
  • Download and Install win-acme
    • Download win-acme from https://www.win-acme.com.
    • After downloading, unblock the files and extract them to C:\win-acme.
  • Run win-acme to Generate SSL Certificates
    • Navigate to C:\win-acme and run win-acme.exe as Administrator.
    • Follow the prompts to select the appropriate site for which you want to generate the SSL certificate.
    • Once complete, your sites will be secured with Let’s Encrypt SSL certificates.

By following these steps, you can manage multiple websites with different domains and subdomains on a single IIS server with Let’s Encrypt SSL certificates, solving the issues typically associated with wildcard certificates for different domains.

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