Self-Hosted ACME Clients Beyond Certbot: GetSSL vs Posh-ACME vs Win-ACME

The ACME (Automatic Certificate Management Environment) protocol, created by Let’s Encrypt, has revolutionized TLS certificate management by enabling fully automated certificate issuance and renewal. While Certbot is the most well-known ACME client, it is not the only option — and for many deployment scenarios, alternative ACME clients offer better platform support, simpler automation, or more flexible challenge handling.

Three mature ACME clients serve distinct niches: GetSSL, a lightweight Bash script designed for automated certificate deployment across remote servers; Posh-ACME, a comprehensive PowerShell module with the widest DNS challenge plugin ecosystem; and Win-ACME (formerly Let’s Encrypt Win Simple), a Windows-native ACME client with IIS integration and interactive GUI.

Why Use Alternative ACME Clients?

Certbot is excellent for standard Linux web server deployments, but alternative ACME clients address specific gaps:

• Platform compatibility — Certbot requires Python, which may not be available or desirable on all systems (Windows, embedded devices, minimal containers)
• Deployment automation — some clients are designed specifically for pushing certificates to multiple remote servers via SSH, SFTP, or API
• DNS challenge breadth — different clients support different sets of DNS provider APIs for DNS-01 validation
• Windows integration — native Windows clients can install certificates directly into IIS, Exchange, or the Windows certificate store
• Minimal dependencies — lightweight clients with no Python or .NET runtime requirements
• Custom workflows — some clients offer hook-based automation that integrates with existing deployment pipelines

For foundational TLS automation, see our cert-manager vs Lego vs ACME.sh certificate automation guide. For ACME DNS challenge deep-dives, our Certbot vs ACME.sh vs Lego vs Dehydrated comparison covers the most popular clients.

GetSSL (srvrco/getssl)

GetSSL is a Bash shell script that obtains free SSL certificates from Let’s Encrypt (or any ACME-compliant CA). It is specifically designed for automating the certificate process on remote servers, making it ideal for multi-server deployments where certificates need to be obtained on one machine and deployed to many.

Key features:

• Pure Bash — no Python, no .NET, no package dependencies beyond curl and openssl
• Automatic certificate renewal via cron
• Remote server deployment via SSH, SFTP, or rsync
• Supports both HTTP-01 and DNS-01 challenges
• DNS challenge plugins for many providers (Cloudflare, AWS Route 53, Google Cloud DNS)
• Multi-domain and wildcard certificate support
• Per-domain configuration files
• Pre/post renewal hooks for service restarts
• Certificate expiry monitoring and email alerts
• Minimal footprint — single script file

GetSSL’s design philosophy is simplicity and portability. It runs on any system with Bash, curl, and openssl — making it suitable for embedded systems, minimal containers, and legacy servers where installing Certbot’s Python dependencies is impractical.

Star count: 2,224+ on GitHub Language: Bash License: GPLv3

Posh-ACME (rmbolger/Posh-ACME)

Posh-ACME is a PowerShell module that acts as a full-featured ACME client with the widest DNS challenge plugin ecosystem of any ACME client. It supports dozens of DNS providers natively, making it the go-to choice for organizations that need DNS-01 validation across diverse DNS infrastructure.

Key features:

• PowerShell module — native on Windows, works on Linux/macOS via PowerShell 7
• 80+ DNS challenge plugins (AWS, Azure, Cloudflare, GoDaddy, Route 53, etc.)
• Supports ACME v2 (RFC 8555) with multiple CAs (Let’s Encrypt, ZeroSSL, BuyPass, Google)
• Certificate order management with multiple domains and SANs
• Automatic renewal scheduling
• Custom deployment scripts via plugin architecture
• PFX/PKCS#12 export for Windows certificate store
• Account key management and rotation
• ACME directory caching for performance
• Cross-platform (Windows, Linux, macOS)

Posh-ACME’s DNS plugin ecosystem is its standout feature. Where Certbot requires separate plugins for each DNS provider (and not all are maintained), Posh-ACME bundles support for dozens of providers in a single module. This makes it particularly valuable for organizations managing DNS across multiple providers.

Star count: 902+ on GitHub Language: PowerShell License: MIT

Win-ACME (win-acme/win-acme)

Win-ACME (formerly Let’s Encrypt Win Simple) is a Windows-native ACME client designed specifically for Windows server environments. It provides seamless integration with IIS, scheduled task-based renewal, and both interactive and non-interactive operation modes.

Key features:

• Native Windows application (.NET) — no WSL, no Cygwin required
• Direct IIS integration — automatically binds certificates to IIS sites
• Scheduled task for automatic renewal
• Interactive menu-driven setup and non-interactive scriptable mode
• DNS challenge plugins for major providers (Cloudflare, AWS, Azure)
• Certificate store installation (LocalMachine/CurrentUser)
• SMTP, FTP, RDP, and Exchange certificate support
• Plugin architecture for custom deployment targets
• Email notifications for renewal events
• Portable executable — no installation required

Win-ACME is the standard ACME client for Windows server administrators who need to manage TLS certificates without leaving the Windows ecosystem. Its IIS integration is particularly valuable — it can automatically detect sites, request certificates, and bind them without manual intervention.

Star count: 5,681+ on GitHub Language: C# (.NET) License: MIT

Comparison Table

Installation and Configuration

Installing GetSSL

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# Download and install
curl -s https://raw.githubusercontent.com/srvrco/getssl/master/getssl > /usr/local/bin/getssl
chmod 755 /usr/local/bin/getssl

# Create configuration for a domain
getssl -c example.com

# Edit configuration file
nano ~/.getssl/example.com/getssl.cfg

# Obtain certificate
getssl example.com

# Set up cron for automatic renewal
echo "0 0 * * * /usr/local/bin/getssl -u -q -a >> /var/log/getssl.log 2>&1" | crontab -

Installing Posh-ACME

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# Install from PowerShell Gallery
Install-Module -Name Posh-ACME -Scope CurrentUser

# Set ACME server (Let's Encrypt production)
Set-PAServer LE_PROD

# Create a new ACME account
New-PAAccount -Contact admin@example.com -AcceptTOS

# Request a certificate with DNS challenge
$pArgs = @{
    CFKey = 'your-cloudflare-api-key'
    CFEmail = 'admin@example.com'
}
New-PACertificate '*.example.com', 'example.com' `
    -DnsPlugin Cloudflare -PluginArgs $pArgs `
    -AcceptTOS -Contact admin@example.com

Installing Win-ACME

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# Download latest release
$url = "https://github.com/win-acme/win-acme/releases/latest/download/win-acme.x64.trimmed.zip"
Invoke-WebRequest -Uri $url -OutFile "win-acme.zip"
Expand-Archive -Path "win-acme.zip" -DestinationPath "C:\win-acme"

# Run interactive mode
cd C:\win-acme
.\wacs.exe

# Non-interactive certificate request for IIS
.\wacs.exe --target iis --siteid 1 --store centralssl `
    --installation iis,centralssl --centralsslstore C:\certs `
    --certificatestore My

Choosing the Right ACME Client

Choose GetSSL when:

• You need to deploy certificates across multiple remote Linux servers
• You want zero dependencies (just Bash, curl, and openssl)
• You are deploying to minimal containers or embedded systems
• You prefer simple shell-script automation over package management

Choose Posh-ACME when:

• You need DNS-01 validation with a wide variety of DNS providers
• You work in mixed Windows/Linux environments with PowerShell
• You want the broadest CA support (Let’s Encrypt, ZeroSSL, BuyPass, Google)
• You need cross-platform certificate management

Choose Win-ACME when:

• You are managing certificates on Windows Server with IIS
• You need native Windows certificate store integration
• You want a portable executable with no installation
• You need interactive setup for initial configuration

Why Self-Host ACME Certificate Management?

Managing certificate automation through self-hosted ACME clients gives organizations complete control over their TLS infrastructure. Rather than relying on managed certificate services or manual renewal processes, self-hosted ACME clients integrate directly into your existing deployment pipelines, ensuring certificates are always valid without human intervention.

Certificate lifecycle management is a common source of outages — expired certificates cause service disruptions that are entirely preventable. Self-hosted ACME clients with automated renewal (via cron, scheduled tasks, or systemd timers) eliminate this risk by checking certificate validity daily and renewing before expiration.

Compliance requirements in regulated industries often mandate that private keys never leave the organization’s infrastructure. Self-hosted ACME clients generate private keys locally on the target server and only transmit Certificate Signing Requests (CSRs) to the CA — the private key never traverses the network. This is a critical security advantage over managed certificate services where key generation may occur on third-party infrastructure.

For monitoring certificate expiration across your infrastructure, our SSL certificate expiration monitoring guide covers complementary monitoring approaches.

FAQ

What is the ACME protocol?

ACME (Automatic Certificate Management Environment) is an IETF standard (RFC 8555) that automates the process of obtaining and renewing TLS certificates. It defines how a client proves domain ownership (via HTTP-01, DNS-01, or TLS-ALPN-01 challenges) and receives a signed certificate from a Certificate Authority.

What is the difference between HTTP-01 and DNS-01 challenges?

HTTP-01 proves domain ownership by placing a verification file on your web server. DNS-01 proves ownership by creating a specific DNS TXT record. DNS-01 is required for wildcard certificates and is preferred when your server is not publicly accessible (behind a firewall or NAT).

Can these ACME clients obtain wildcard certificates?

Yes, all three clients support wildcard certificates via DNS-01 challenge. HTTP-01 challenge does not support wildcards — only DNS-01 can prove ownership of all subdomains simultaneously.

How does certificate renewal work automatically?

Each client provides a mechanism for scheduled renewal: GetSSL uses cron jobs, Posh-ACME uses PowerShell scheduled tasks or systemd timers, and Win-ACME creates Windows Scheduled Tasks. The client checks certificate expiry dates and renews when certificates are within 30 days of expiration.

Can I use these clients with CAs other than Let’s Encrypt?

Yes. GetSSL supports any ACME v2-compatible CA. Posh-ACME explicitly supports Let’s Encrypt, ZeroSSL, BuyPass, and Google. Win-ACME supports Let’s Encrypt and other ACME v2 CAs. You configure the ACME directory URL to point to your preferred CA.

Is GetSSL secure for multi-server deployment?

GetSSL uses SSH for remote certificate deployment, which is secure when properly configured with key-based authentication. The private key is generated on the target server and never transmitted over the network — only the CSR (which contains no secret material) is sent to the CA.