~~NOTOC~~
====== Scenario 10.3: mTLS Deployment ======

<WRAP round info>
**Category:** [[.:start|TLS/mTLS]] \\
**Complexity:** ⭐⭐⭐⭐ (High) \\
**Prerequisites:** Server and client certificates, PKI \\
**Estimated Time:** 30-45 Minutes
</WRAP>

----

===== Description =====

This scenario describes the **complete deployment of an mTLS infrastructure** for mutual authentication between clients and servers.

**Use Cases:**
  * Zero-Trust Architectures
  * Service Mesh (Istio, Linkerd)
  * API Security
  * Microservices Communication
  * IoT Device Authentication

----

===== Architecture =====

<mermaid>
flowchart TD
    subgraph PKI
        ROOT[Root CA] --> INT_SRV[Intermediate CA Server]
        ROOT --> INT_CLI[Intermediate CA Clients]
    end

    subgraph Server
        INT_SRV --> SRV_CERT[Server Certificate]
        SRV_CERT --> API[API Server]
    end

    subgraph Clients
        INT_CLI --> CLI1[Client 1]
        INT_CLI --> CLI2[Client 2]
        INT_CLI --> CLI3[Service A]
    end

    CLI1 <-->|mTLS| API
    CLI2 <-->|mTLS| API
    CLI3 <-->|mTLS| API
</mermaid>

----

===== 1. PKI Structure for mTLS =====

<code csharp>
using WvdS.Security.Cryptography.X509Certificates.Extensions.PQ;

public class MtlsPkiSetup
{
    public void CreateMtlsPki(string basePath)
    {
        using var ctx = PqCryptoContext.Initialize();

        // Root CA
        using var rootKey = ctx.GenerateKeyPair(PqAlgorithm.MlDsa65);
        var rootCert = ctx.CreateSelfSignedCertificate(
            rootKey,
            new DnBuilder().AddCN("mTLS Root CA").AddO("Example").Build(),
            validDays: 3650,
            extensions: new ExtBuilder()
                .BasicConstraints(ca: true, pathLengthConstraint: 2, critical: true)
                .KeyUsage(KeyUsageFlags.KeyCertSign | KeyUsageFlags.CrlSign, critical: true)
                .Build()
        );
        SaveCertAndKey(basePath, "root-ca", rootCert, rootKey);

        // Server Intermediate CA
        using var serverIntKey = ctx.GenerateKeyPair(PqAlgorithm.MlDsa65);
        var serverIntCert = CreateIntermediateCa(
            ctx, rootCert, rootKey, serverIntKey,
            "mTLS Server Intermediate CA",
            new[] { "dns:.example.com" }  // Name Constraint
        );
        SaveCertAndKey(basePath, "server-int-ca", serverIntCert, serverIntKey);

        // Client Intermediate CA
        using var clientIntKey = ctx.GenerateKeyPair(PqAlgorithm.MlDsa65);
        var clientIntCert = CreateIntermediateCa(
            ctx, rootCert, rootKey, clientIntKey,
            "mTLS Client Intermediate CA",
            null  // No name constraints for clients
        );
        SaveCertAndKey(basePath, "client-int-ca", clientIntCert, clientIntKey);

        Console.WriteLine("mTLS PKI created");
    }
}
</code>

----

===== 2. Server Configuration =====

<code csharp>
// ASP.NET Core Kestrel mTLS
builder.WebHost.ConfigureKestrel(options =>
{
    options.ListenAnyIP(443, listenOptions =>
    {
        listenOptions.UseHttps(httpsOptions =>
        {
            // Server certificate
            httpsOptions.ServerCertificate = new X509Certificate2(
                "server.pfx", "ServerPassword!");

            // Require client certificate
            httpsOptions.ClientCertificateMode = ClientCertificateMode.RequireCertificate;

            // Accepted client CAs
            httpsOptions.ClientCertificateValidation = (cert, chain, errors) =>
            {
                // Only accept certificates from our client CA
                return ValidateClientCertificate(cert, chain);
            };
        });
    });
});

bool ValidateClientCertificate(X509Certificate2 cert, X509Chain? chain)
{
    // Load trusted client CA
    var trustedClientCa = new X509Certificate2("client-int-ca.crt.pem");

    // Build custom chain
    var customChain = new X509Chain();
    customChain.ChainPolicy.CustomTrustStore.Add(trustedClientCa);
    customChain.ChainPolicy.TrustMode = X509ChainTrustMode.CustomRootTrust;
    customChain.ChainPolicy.RevocationMode = X509RevocationMode.Online;

    // Check Extended Key Usage: clientAuth
    customChain.ChainPolicy.ApplicationPolicy.Add(
        new Oid("1.3.6.1.5.5.7.3.2"));

    return customChain.Build(cert);
}
</code>

----

===== 3. Client Configuration =====

<code csharp>
public HttpClient CreateMtlsClient(string clientCertPath, string clientKeyPath, string password)
{
    using var ctx = PqCryptoContext.Initialize();

    // Load client certificate
    var clientCert = ctx.LoadCertificateWithPrivateKey(
        clientCertPath,
        clientKeyPath,
        password
    );

    // Server trust store
    var trustedServerCa = ctx.LoadCertificate("server-int-ca.crt.pem");

    var handler = new HttpClientHandler
    {
        ClientCertificateOptions = ClientCertificateOption.Manual,
        SslProtocols = SslProtocols.Tls13,

        ServerCertificateCustomValidationCallback = (message, cert, chain, errors) =>
        {
            var customChain = new X509Chain();
            customChain.ChainPolicy.CustomTrustStore.Add(trustedServerCa);
            customChain.ChainPolicy.TrustMode = X509ChainTrustMode.CustomRootTrust;

            // Extended Key Usage: serverAuth
            customChain.ChainPolicy.ApplicationPolicy.Add(
                new Oid("1.3.6.1.5.5.7.3.1"));

            return customChain.Build(cert);
        }
    };

    handler.ClientCertificates.Add(clientCert);

    return new HttpClient(handler)
    {
        DefaultRequestHeaders = { { "User-Agent", "mTLS-Client/1.0" } }
    };
}
</code>

----

===== 4. Nginx mTLS Reverse Proxy =====

<code nginx>
server {
    listen 443 ssl http2;
    server_name api.example.com;

    # Server certificate
    ssl_certificate     /etc/nginx/ssl/server-chain.pem;
    ssl_certificate_key /etc/nginx/ssl/server.key.pem;

    # Client authentication
    ssl_client_certificate /etc/nginx/ssl/client-ca-chain.pem;
    ssl_verify_client on;
    ssl_verify_depth 2;

    # CRL checking
    ssl_crl /etc/nginx/ssl/client-ca.crl;

    # TLS 1.3
    ssl_protocols TLSv1.3;
    ssl_prefer_server_ciphers off;

    # OCSP Stapling for server cert
    ssl_stapling on;
    ssl_stapling_verify on;

    location / {
        # Forward client info to backend
        proxy_set_header X-Client-Cert-Subject $ssl_client_s_dn;
        proxy_set_header X-Client-Cert-Issuer $ssl_client_i_dn;
        proxy_set_header X-Client-Cert-Serial $ssl_client_serial;
        proxy_set_header X-Client-Cert-Fingerprint $ssl_client_fingerprint;
        proxy_set_header X-Client-Verify $ssl_client_verify;

        proxy_pass http://backend:8080;
    }
}
</code>

----

===== 5. Kubernetes mTLS (Istio) =====

<code yaml>
# PeerAuthentication - mTLS for all services in namespace
apiVersion: security.istio.io/v1beta1
kind: PeerAuthentication
metadata:
  name: default
  namespace: production
spec:
  mtls:
    mode: STRICT  # mTLS mandatory
---
# DestinationRule - mTLS for outgoing connections
apiVersion: networking.istio.io/v1beta1
kind: DestinationRule
metadata:
  name: default
  namespace: production
spec:
  host: "*.production.svc.cluster.local"
  trafficPolicy:
    tls:
      mode: ISTIO_MUTUAL  # Istio-managed certificates
---
# AuthorizationPolicy - Certificate-based authorization
apiVersion: security.istio.io/v1beta1
kind: AuthorizationPolicy
metadata:
  name: api-access
  namespace: production
spec:
  selector:
    matchLabels:
      app: api-server
  action: ALLOW
  rules:
  - from:
    - source:
        principals: ["cluster.local/ns/production/sa/frontend-service"]
        namespaces: ["production"]
</code>

----

===== 6. Monitoring and Logging =====

<code csharp>
public class MtlsLoggingMiddleware
{
    private readonly RequestDelegate _next;
    private readonly ILogger<MtlsLoggingMiddleware> _logger;

    public MtlsLoggingMiddleware(RequestDelegate next, ILogger<MtlsLoggingMiddleware> logger)
    {
        _next = next;
        _logger = logger;
    }

    public async Task InvokeAsync(HttpContext context)
    {
        var clientCert = context.Connection.ClientCertificate;

        if (clientCert != null)
        {
            _logger.LogInformation(
                "mTLS Request: Subject={Subject}, Thumbprint={Thumbprint}, " +
                "Serial={Serial}, NotAfter={NotAfter}",
                clientCert.Subject,
                clientCert.Thumbprint,
                clientCert.SerialNumber,
                clientCert.NotAfter
            );

            // Warning for soon-expiring certificates
            var daysUntilExpiry = (clientCert.NotAfter - DateTime.UtcNow).Days;
            if (daysUntilExpiry < 30)
            {
                _logger.LogWarning(
                    "Client certificate expires in {Days} days: {Subject}",
                    daysUntilExpiry,
                    clientCert.Subject
                );
            }
        }

        await _next(context);
    }
}
</code>

----

===== Industry-Specific mTLS Deployments =====

^  Industry  ^  Infrastructure  ^  Certificate Rotation  ^  Special Feature  ^
| **Cloud Native** | Istio/Linkerd | Automatic (SPIFFE) | Service Mesh |
| **Financial Sector** | Hardware LB | 90 days | HSM-backed |
| **Healthcare** | On-Premise | 1 year | Air-gap capable |
| **IoT** | Edge Gateway | 2-5 years | Offline capable |

----

===== Related Scenarios =====

^  Relationship  ^  Scenario  ^  Description  ^
| **Prerequisite** | [[.:server_setup|10.1 TLS Server]] | Server side |
| **Prerequisite** | [[.:client_config|10.2 TLS Client]] | Client side |
| **Related** | [[en:int:pqcrypt:szenarien:authentifizierung:mtls_client_auth|9.1 mTLS Auth]] | Authentication |
| **Extension** | [[.:hybrid_tls|10.4 Hybrid TLS]] | PQ upgrade |

----

<< [[.:client_config|← 10.2 TLS Client]] | [[.:start|↑ TLS Overview]] | [[.:hybrid_tls|10.4 Hybrid TLS →]] >>

{{tag>scenario tls mtls deployment kubernetes istio}}

----
//Wolfgang van der Stille @ EMSR DATA d.o.o. - Post-Quantum Cryptography Professional//