Deep Dive: How ACME Azure Automates SSL Certificate Management

Let’s dive deep into how ACME Azure manages SSL certificates automatically. We’ll explore the entire process from initialization to renewal.

The Certificate Management Lifecycle

1. Initialization & Configuration

When ACME Azure starts, it:

1. Loads environment variables for configuration
2. Validates required settings (domains, email, Azure credentials)
3. Sets up the HTTP-01 challenge server on port 80
4. Establishes connection to Azure Key Vault

2. Certificate Check Process

Every CHECK_INTERVAL (default: 24h), the application:

// Pseudocode of the main check loop
for {
    // Check if certificate exists and needs renewal
    needsRenewal = checkIfRenewalNeeded(keyVaultName, certName, renewBeforeDays)
    
    if needsRenewal {
        // Generate new certificate
        processCertificates(domains, email, keyVaultName, certName)
    }
    
    sleep(checkInterval)
}

3. Certificate Generation

When a new certificate is needed, the process follows these steps:

a) ACME Account Setup

• Generates 2048-bit RSA key pair
• Registers with Let’s Encrypt
• Accepts Terms of Service automatically

b) Domain Validation

• Creates HTTP-01 challenge tokens
• Serves tokens at /.well-known/acme-challenge/{token}
• Waits for Let’s Encrypt validation

c) Certificate Issuance

• Requests certificate for all domains
• Receives signed certificate chain
• Converts to PFX format using OpenSSL

4. Azure Key Vault Integration

The certificate storage process:

1. PFX Conversion

// Convert certificate and private key to PFX
pfxData = convertToPFX(
    certPEM,      // Certificate chain
    keyPEM,       // Private key
    pfxPassword   // Optional password
)

2. Key Vault Upload

// Upload to Azure Key Vault
client.ImportCertificate(
    certName,
    base64(pfxData),
    password
)

5. Error Handling & Notifications

The application implements comprehensive error handling:

Error occurs
  │
  ├─► Log error details
  │
  ├─► Check if notifications enabled
  │     │
  │     └─► Send email notification
  │
  └─► Continue monitoring

Technical Components

HTTP-01 Challenge Handler

// HTTP challenge configuration
http01.NewProviderServer("", "80")
    ├── Creates temporary challenge files
    ├── Serves files at /.well-known/acme-challenge/
    └── Cleans up after validation

Certificate Monitoring

The application checks certificates using:

expiresOn = currentCert.Attributes.Expires
renewalDate = expiresOn - renewBeforeDays

if currentDate > renewalDate {
    trigger renewal process
}

Error Notification System

When errors occur:

1. Captures full error context
2. Formats message with domain and error details
3. Sends via configured SMTP server
4. Logs delivery status

Memory & Storage Management

ACME Azure maintains minimal state:

• No local certificate storage
• Temporary files for ACME challenges
• In-memory process tracking

All persistent storage is handled by Azure Key Vault, making the application stateless and container-friendly.

Performance Considerations

The application is designed to be lightweight:

• Single goroutine for certificate monitoring
• On-demand certificate generation
• Minimal memory footprint (~50MB)
• Low CPU usage except during certificate operations

Security Measures

1. Private Key Handling

   • Keys generated in memory
   • Never written to disk unencrypted
   • Immediately converted to PFX

2. Azure Integration

   • Uses Azure SDK secure practices
   • Supports managed identities
   • Minimal required permissions

3. ACME Protocol

   • Standards-compliant implementation
   • Secure key generation
   • Automatic protocol version selection

Conclusion

ACME Azure’s architecture ensures reliable, secure certificate management with minimal overhead. The stateless design and comprehensive error handling make it ideal for containerized environments, while the Azure Key Vault integration provides enterprise-grade security for certificate storage.

For implementation details, check the source code at the GitHub repository.