Add SSL certificate checker

Implement SSL certificate checking functionality

server/service-operation/operations/ssl_validator.go

@@ -0,0 +1,65 @@
+package operations
+
+import (
+	"crypto/x509"
+	"fmt"
+	"time"
+)
+
+// validateCertificate performs comprehensive certificate validation
+func (op *SSLOperation) validateCertificate(cert *x509.Certificate, hostname string) error {
+	now := time.Now()
+	
+	// Check if certificate is expired or not yet valid
+	if now.Before(cert.NotBefore) {
+		return fmt.Errorf("certificate is not yet valid (valid from: %v)", cert.NotBefore.Format("2006-01-02 15:04:05"))
+	}
+	if now.After(cert.NotAfter) {
+		return fmt.Errorf("certificate has expired (expired on: %v)", cert.NotAfter.Format("2006-01-02 15:04:05"))
+	}
+	
+	// Verify hostname matches certificate
+	if err := cert.VerifyHostname(hostname); err != nil {
+		return fmt.Errorf("hostname verification failed: %v", err)
+	}
+	
+	// Check key usage - certificates should have digital signature capability
+	if cert.KeyUsage&x509.KeyUsageDigitalSignature == 0 {
+		return fmt.Errorf("certificate missing required digital signature key usage")
+	}
+	
+	// Check if certificate is self-signed (basic check)
+	if cert.Issuer.CommonName == cert.Subject.CommonName && len(cert.Subject.Organization) == 0 {
+		return fmt.Errorf("certificate appears to be self-signed")
+	}
+	
+	// Validate certificate chain if intermediate certificates are present
+	if err := op.validateCertificateChain(cert); err != nil {
+		return fmt.Errorf("certificate chain validation failed: %v", err)
+	}
+	
+	return nil
+}
+
+// validateCertificateChain performs basic certificate chain validation
+func (op *SSLOperation) validateCertificateChain(cert *x509.Certificate) error {
+	// Check if the certificate has proper extensions for SSL/TLS
+	hasServerAuth := false
+	for _, usage := range cert.ExtKeyUsage {
+		if usage == x509.ExtKeyUsageServerAuth {
+			hasServerAuth = true
+			break
+		}
+	}
+	
+	if !hasServerAuth {
+		return fmt.Errorf("certificate does not have server authentication extension")
+	}
+	
+	// Check certificate version (should be v3 for modern certificates)
+	if cert.Version < 3 {
+		return fmt.Errorf("certificate version %d is outdated (should be v3)", cert.Version)
+	}
+	
+	return nil
+}