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WinCertes - ACME Client for Windows

WinCertes is a simple ACMEv2 Client for Windows, able to manage the automatic issuance and renewal of SSL Certificates, for IIS or other web servers. It is based on Certes Library. Pre-compiled binaries are available from GitHub (just look for the standard GitHub menu entry).

GPLv3 License


  • Windows Server 2008 R2 SP1 or higher (.Net 4.6.1 or higher), 64-bit


  • CLI-based for easy integration with DevOps
  • Easy certificate requests & automated SSL bindings
  • Auto renewal using Scheduled Task
  • SAN support (multi-domain certificates)
  • Full support for ACMEv2, including Wildcard Certificate support (* [*]
  • Optional powershell scripting for advanced deployment (Exchange, multi-server, etc)
  • HTTP challenge validation.
    • Built-in Http Challenge Server for easier configuration of challenge responses
    • Ability to support already installed web server (by default IIS) to provide challenge responses
  • DNS challenge validation
    • Support for Windows DNS Server
    • Support for acme-dns
    • Support for AWS Route53
  • Import of certificate and key into chosen CSP/KSP, enabling compatibility with HSMs
  • Support of any ACMEv2 compliant CA, including Let's Encrypt and Let's Encrypt Staging (for tests/dry-run)
  • Windows Installer for easy deployment
  • Configuration is stored in Registry
  • Support for certificate revocation
  • Logs activity to STDOUT and file

[*] Warning: Let's Encrypt does not allow wildcard certificates issuance with HTTP validation. So, the DNS validation mode MUST be used to retrieve wildcard certificate.

This OpenSource software is brought to you by EverTrust, which provides support plans for it as part of EverTrust Horizon software suite.

Quick Start (IIS users)

  1. Download from GitHub and install it.
  2. Launch a command line (cmd.exe) as Administrator
  3. Enter the following command:
WinCertes.exe -e -d -d -w=c:\inetpub\wwwroot -b "Default Web Site" -p

And... That's all! The certificate is requested from Let's Encrypt, and bound to IIS' Default Web Site

Advanced users can explore the different validation modes, deployment modes and other advanced options. See Registry Settings regarding advanced options and DNS validation modes.

Command Line Options

  -s, --service=VALUE        the ACME Service URI to be used (optional,
                               defaults to Let's Encrypt)
  -e, --email=VALUE          the account email to be used for ACME requests (
                               optional, defaults to no email)
  -d, --domain=VALUE         the domain(s) to enroll (mandatory)
  -w, --webserver[=ROOT]     toggles the local web server use and sets its ROOT
                               directory (default c:\inetpub\wwwroot).
                               Activates HTTP validation mode.
  -p, --periodic             should WinCertes create the Windows Scheduler task
                               to handle certificate renewal (default=no)
  -b, --bindname=VALUE       IIS site name to bind the certificate to, e.g. "
                               Default Web Site". Defaults to no binding.
  -n, --bindport=VALUE       IIS site port to bind the certificate to, e.g. 443. 
                               Defaults to 443, used only if -b is specified.
  -f, --scriptfile=VALUE     PowerShell Script file e.g. "C:\Temp\script.ps1"
                               to execute upon successful enrollment (default=
  -a, --standalone           should WinCertes create its own WebServer for
                               validation. Activates HTTP validation mode.
                               WARNING: it will use port 80 unless -l is
  -r, --revoke[=REASON]      should WinCertes revoke the certificate identified
                               by its domains (to be used only with -d). REASON
                               is an optional integer between 0 and 5.
  -k, --csp=VALUE            import the certificate into specified csp. By
                               default WinCertes imports in the default CSP.
  -t, --renewal=N            trigger certificate renewal N days before
                               expiration, default 30
  -l, --listenport=N         listen on port N in standalone mode (for use with -
                               a switch, default 80)
      --show                 show current configuration parameters
      --reset                reset all configuration parameters
      --extra[=VALUE]        manages additional certificate(s) instead of the
                               default one, with its own settings. Add an
                               integer index optionally to manage more certs.
      --no-csp               does not import the certificate into CSP. Use with
                               caution, at your own risks. REVOCATION WILL NOT
                               WORK IN THAT MODE.
      --setopt=VALUE1:VALUE2 sets configuration options in the form key:value.

Typical usage: WinCertes.exe -a -e -d -d -p
This will automatically create and register account with email, and
request the certificate for and, then import it into
Windows Certificate store (machine context), and finally set a Scheduled Task to manage renewal.

"WinCertes.exe -d -d -r" will revoke that certificate.

Using Non-Let's Encrypt CA

By default, WinCertes uses Let's Encrypt (LE) CA to issue SSL certificates. However there are several cases in which one would like to use another CA:

  1. You're testing the certificate deployment for LE: add -s to the command line
  2. You want to use another public CA: add -s to the command line
  3. You want to use an internal ACMEv2 compliant CA: deploy the internal CA certificates to the Windows Trusted CA store, and add -s https://internal-ca-acmev2.example.corp to the command line. If you need a solution to give ACMEv2 capabilities to your internal PKI, you can check e.g. EverTrust Horizon.

About PowerShell Scripting

WinCertes gives the option to launch a PowerShell script upon successfull enrollment. This script will receive two parameters:

  • pfx: contains the full path to the PFX (PKCS#12) file
  • pfwPassword: contains the password required to parse the PFX

The PFX can then be parsed using e.g. Get-PfxData, and later on re-exported with different pasword, or imported within a different Windows store.

The following code is a simple example of PowerShell script that you can call from WinCertes:


# Build the pfx object using file path and password
$mypwd = ConvertTo-SecureString -String $pfxPassword -Force -AsPlainText
$mypfx = Get-PfxData -FilePath $pfx -Password $mypwd

# Start the real work. Here we simply append the certificate DN to a text file
$mypfx.EndEntityCertificates.Subject | Out-File -FilePath c:\temp\test.txt -Append

# Copy certificate: here's an example for Apache
Copy-Item -Path $cer -Destination C:\\Program\ Files\\Apache\ Group\\Apache2\\conf\\server.crt
Copy-Item -Path $key -Destination C:\\Program\ Files\\Apache\ Group\\Apache2\\conf\\server.key

About IIS Configuration

WinCertes can auto-configure IIS regarding the SSL certificate and its bindings (see below for more details). However, IIS configuration needs to be modified in order for WinCertes HTTP validation to work: WinCertes requires the "*" mimetype to be set, else IIS will refuse to serve the challenge file. WinCertes tries to do this automatically as well, but it might fail depending on your version and setup of IIS.

It is possible to fix the issue permanently:

  • using the IIS Management Console, in the "MIME Types" section
  • or by adding/modifying the web.config file at the document root of IIS, with the following content:
<?xml version="1.0" encoding="UTF-8"?>
            <mimeMap fileExtension=".*" mimeType="application/octet-stream" />
            <mimeMap fileExtension="." mimeType="application/octet-stream" />

About IIS Bindings

The logic for the IIS bindings is the following, executed after the certificate has been issued from the ACME server:

  • list all the SubjectAlternativeNames in the certificate, and for each of them:
    • for the website whose name is given by the "-b" switch, list the existing https bindings:
      • if there is none, create one with port 443
      • if there are bindings, update them using the new certificate

Therefore if you wish to have IIS listen on non-standard ports:

  1. issue the certificate the first time using WinCertes and the "-b" option pointing at the right site
  2. edit the bindings and add/modify them to suit your needs: WinCertes will keep these settings upon renewal


Usually when the enrollment fails you can get more information in the latest error message given by WinCertes. Most of the time it should look like:

Failed to register and validate order with CA: Could not validate challenge: Could not resolve DNS name

Most common causes are:

  • When using the "standalone" mode (-a switch), the Windows Firewall gets in the way. Try to fully deactivate it.
  • When not using the "standalone" mode, the Web Server document root is not specified correctly: use the -w switch.
  • You made too many tests on the LE production server. Remember to add -s to the command line when you test the enrollment!
  • After testing you need to reinitialize WinCertes context: delete all registry keys under HKLM\Software\WinCertes

Development & Bug Reporting

If you have a bug or feature and you can fix the problem yourself please just:

  1. File a new issue
  2. Fork the repository
  3. Make your changes
  4. Submit a pull request, detailing the problem being solved and testing steps/evidence

If you cannot provide a fix for the problem yourself, please file an issue and describe the fault with steps to reproduce.

The development requires Visual Studio 2017 or 2019, and Wix if you want to build the installer.

This project is (c) 2018-2019 Alexandre Aufrere

Released under the terms of GPLv3