When implementing DNS-based routing for multi-tenant documentation systems, the SSL/TLS certificate handling becomes critical. The specific scenario involves:

Tenant Domain: docs.tenantcompany.com (CNAME) 
→ 
Hosted Domain: docs.tenant.mycompany.com

The SSL handshake occurs after DNS resolution, meaning the certificate must validate against the client-requested domain (docs.tenantcompany.com). A wildcard certificate for *.tenantcompany.com would technically cover this case, but proper configuration is essential.

Option 1: Tenant-Provided Certificate

If tenants manage their own certificates:

server {
    listen 443 ssl;
    server_name docs.tenant.mycompany.com docs.tenantcompany.com;
    
    # Tenant's wildcard cert
    ssl_certificate /path/to/tenant_wildcard.pem;
    ssl_certificate_key /path/to/tenant_wildcard.key;
    
    # SAN must include both domains
    ssl_client_certificate /path/to/ca-bundle.crt;
}

Option 2: Automated Certificate Management

For scalable solutions, consider Let's Encrypt with DNS challenges:

# Certbot example for Nginx
certbot --nginx \
  -d docs.tenantcompany.com \
  -d docs.tenant.mycompany.com \
  --preferred-challenges dns \
  --manual-auth-hook ./authenticator.sh \
  --manual-cleanup-hook ./cleanup.sh

• Certificate Transparency Log requirements for new domains
• TLS SNI (Server Name Indication) support in legacy clients
• CAA record conflicts in tenant DNS zones

For large-scale implementations, a Kubernetes ingress controller with cert-manager handles this elegantly:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: tenant-docs
  annotations:
    cert-manager.io/cluster-issuer: letsencrypt-prod
spec:
  tls:
  - hosts:
    - docs.tenantcompany.com
    - docs.tenant.mycompany.com
    secretName: tenant-tls
  rules:
  - host: docs.tenantcompany.com
    http:
      paths: [...]
  - host: docs.tenant.mycompany.com
    http:
      paths: [...]

In multi-tenant architectures where documentation is served through tenant-specific subdomains, the DNS configuration typically involves CNAME records pointing tenant domains to your infrastructure. The SSL/TLS handshake occurs before any HTTP redirection, which creates certificate validation requirements.

When a user accesses docs.tenantcompany.com, the TLS handshake validates the certificate against these criteria:

1. Certificate must cover exact FQDN (docs.tenantcompany.com) or
2. Wildcard certificate covering *.tenantcompany.com
3. Certificate must chain to a trusted root CA
4. Must pass SNI validation if using shared hosting

A tenant's existing wildcard certificate for *.tenantcompany.com will work for your CNAME setup, provided:

# Example openssl verification
openssl s_client -connect docs.tenantcompany.com:443 \
  -servername docs.tenantcompany.com | \
  openssl x509 -noout -text | \
  grep "DNS:*.tenantcompany.com"

When wildcards aren't available, consider these approaches:

# Option 1: SNI-based certificate loading
server {
    listen 443 ssl;
    server_name docs.tenantcompany.com;
    ssl_certificate /path/to/tenant_cert.pem;
    ssl_certificate_key /path/to/tenant_key.pem;
    # ... other config
}

For automated certificate management:

# Example using Certbot with DNS challenge
import certbot.main

certbot.main.main([
    'certonly',
    '--dns-route53',
    '--domain', 'docs.tenantcompany.com',
    '--non-interactive',
    '--agree-tos',
    '-m', 'admin@tenantcompany.com'
])

Key considerations for production environments:

• Ensure DNS TTL values are optimized (300-600 seconds)
• Monitor certificate expiration (90-day lifecycle for Let's Encrypt)
• Implement OCSP stapling for performance

Example monitoring check:

#!/bin/bash
expiry_date=$(echo | \
  openssl s_client -connect docs.tenantcompany.com:443 2>/dev/null | \
  openssl x509 -noout -dates | \
  grep 'notAfter' | \
  cut -d'=' -f2)

remaining_days=$(( ($(date -d "$expiry_date" +%s) - $(date +%s)) / 86400 ))