Enabling TLS Without MTLS In Temporal .NET SDK

by Marco 47 views

Hey guys, if you're trying to set up TLS in your Temporal .NET SDK without using mTLS, you might run into some issues. Let's break down the problem and find a solution, shall we? This is a common scenario, especially when you're deploying a self-hosted Temporal server and want to expose it to the internet through a gateway like Istio.

Understanding the Scenario: Client, Gateway, and Temporal Server

Alright, let's paint a picture. Imagine this: you have a client that needs to communicate with your Temporal server. But, you don't want to expose your Temporal server directly to the wild world of the internet. Instead, you put an Istio gateway in front of it. The client connects to the gateway using HTTPS (TLS), the gateway handles the TLS termination and then talks to your Temporal server using plain HTTP. You've also set up an authorizer, so you don't necessarily need mTLS for authentication. You only want the secure transport layer.

This setup is pretty common. The client talks to the gateway, which handles the TLS connection and forwards the traffic to your Temporal server. This is a great way to add an extra layer of security. The goal is to set up a secure connection between your client and the Istio gateway using TLS. The gateway will then communicate with the Temporal server over plain HTTP. Sounds good, right? But here's where things get tricky.

The Problem: The Dreaded InvalidCertificate(UnknownIssuer) Error

So, you've tested your setup using tools like curl and everything seems to work fine. You can establish a TLS connection to the Temporal server through the gateway. However, when you try to use the .NET SDK, you hit a roadblock. You get this error message: 'Connection failed: Server connection error: tonic::transport::Error(Transport, ConnectError(Custom { kind: InvalidData, error: InvalidCertificate(UnknownIssuer) }))'

This error message is a bit cryptic, but basically, it means the SDK is having trouble validating the certificate. It's saying it doesn't trust the issuer of the certificate. Even if you think you've set up TLS correctly, the SDK might still be expecting mTLS or other security configurations that aren't in place in your setup.

The Initial Attempt: config.Tls = new TlsOptions();

Naturally, you might think, "Okay, I'll just enable TLS using config.Tls = new TlsOptions();". You'd assume this would be enough to tell the SDK to use TLS without mTLS. However, as the error message suggests, it's not that simple. The SDK seems to be looking for something more, likely because it still expects some form of certificate verification, even if mTLS isn't strictly required.

Why This Matters

This is important because the .NET SDK doesn't seem to provide a straightforward way to disable certificate verification or to tell it to trust the certificate presented by your gateway without additional configurations. This can be a stumbling block if you're trying to implement a secure, but not overly complex, setup.

Deep Dive: Unpacking the Error and Possible Solutions

Let's dive deeper into the error and look at some possible solutions. We need to understand why the SDK is throwing this error and how we can make it work with our setup. The core of the problem is the SDK's expectation of a certain level of certificate validation that doesn't align with your configuration. The error InvalidCertificate(UnknownIssuer) tells us that the SDK does not recognize or trust the certificate authority that issued the certificate for your Temporal server. This often happens when the SDK is expecting mTLS, where both the client and server present certificates, and each validates the other.

Understanding Certificate Authorities (CAs)

Before we get into solutions, let's briefly talk about Certificate Authorities (CAs). CAs are trusted entities that issue digital certificates. These certificates verify the identity of a server (or client). When a client connects to a server, the server presents its certificate, and the client uses the CA's public key to verify the certificate's authenticity. In the context of your setup, the SDK is likely not recognizing the CA that issued the certificate for your Istio gateway (or Temporal server). This lack of trust leads to the InvalidCertificate(UnknownIssuer) error.

Potential Solutions: Tweaking the SDK

Here are some strategies you can consider to solve this problem:

  1. Configure the SDK to Trust Your CA: The most direct approach is to configure the .NET SDK to trust the Certificate Authority (CA) that signed your server's certificate. You will need to provide the SDK with the CA's certificate. This way, the SDK will be able to validate the server's certificate. You can do this by setting the TlsOptions.CaCert property. However, the configuration will depend on where your CA's certificate is stored. You'll need to load the certificate into the SDK's configuration. This is probably the best option for security because you're explicitly telling the SDK which CA to trust.

  2. Bypass Certificate Validation (Not Recommended for Production): Warning: This is not recommended for production environments, but for testing purposes, you might be able to disable certificate validation. This should only be considered for development and testing, as it removes a critical layer of security. The .NET SDK might have an option to disable certificate validation, or you might need to modify the underlying gRPC configuration (if you're using gRPC for communication). However, be aware that disabling certificate validation can expose your application to man-in-the-middle attacks, where malicious actors can intercept and tamper with your traffic.

  3. mTLS Configuration: Although you don't want mTLS, it might be worth investigating the mTLS configuration. You may be able to set up mTLS between the gateway and the Temporal server without impacting the client-gateway connection. If you can make the connection between the gateway and the server mTLS, you could potentially satisfy the SDK's expectations without changing anything on the client side.

Detailed Implementation of Solution 1: Trusting Your CA

Let's walk through how to configure the SDK to trust your CA, as it's the most secure and recommended approach. First, you need to obtain the CA certificate. This is typically a .crt or .pem file. If you're using a self-signed certificate, you'll need to use the certificate of the CA that signed the certificate. Then, you can add the following code:

using Temporalio.Client;
using Temporalio.Common;

// Assuming you have your CA certificate as a string or byte array
string caCert = "-----BEGIN CERTIFICATE-----\n...YOUR_CA_CERTIFICATE...\n-----END CERTIFICATE-----";

var options = new TlsOptions
{
    CaCert = caCert,
};

var client = await TemporalClient.ConnectAsync(new TemporalClientOptions
{
    Tls = options,
    // ... other options like TargetHost etc.
});

// Now, use the client to interact with Temporal

In this example:

  • You load the CA certificate into a string variable named caCert. Make sure you include the entire certificate content, including the BEGIN CERTIFICATE and END CERTIFICATE lines.
  • You create a TlsOptions instance and set the CaCert property with the caCert string.
  • You pass the TlsOptions instance to the TemporalClientOptions during client creation.

This will configure the .NET SDK to trust the provided CA certificate when establishing a TLS connection.

Considerations and Best Practices

  • Security: Always prioritize security. Make sure your CA certificate is handled securely and is not exposed in your code or configuration in a way that could compromise it.
  • Certificate Management: Implement a proper certificate management process. Regularly renew your certificates and rotate them when necessary. Use a secrets management solution to store and manage your CA certificate.
  • Error Handling: Implement robust error handling to catch exceptions during the TLS connection. This is particularly important for debugging and for responding to certificate-related issues.
  • Testing: Thoroughly test your configuration in various environments before deploying to production. Ensure your SDK can connect to Temporal successfully.

Troubleshooting Tips and Further Exploration

Debugging the Connection

If you're still having issues, try these debugging steps:

  1. Verify Certificate Details: Double-check the certificate details. Ensure the TargetHost in your SDK configuration matches the Common Name (CN) or Subject Alternative Name (SAN) of the server's certificate. If there is a mismatch, you will encounter connection problems.
  2. Check Network Connectivity: Ensure that the client can reach the Istio gateway and that the gateway can reach the Temporal server. Use tools like ping, traceroute, or telnet to verify network connectivity.
  3. Review Istio Gateway Configuration: Make sure your Istio gateway is configured correctly for TLS termination and forwarding to the Temporal server. Check the gateway's logs for any errors.
  4. Enable SDK Logging: Enable verbose logging in your .NET SDK to see more details about the connection process and any errors that occur. Look for specific error messages that provide additional clues.
  5. Consult Documentation and Community: If you're still stuck, refer to the official Temporal .NET SDK documentation and community forums. There might be specific solutions or examples related to your setup.

Advanced Topics

  • gRPC Configuration: The Temporal .NET SDK uses gRPC for communication. You might need to dive deeper into gRPC configuration options to customize the TLS settings further. For example, you may need to use a custom HttpClientHandler to provide additional configuration for TLS, such as specifying client certificates.
  • Secrets Management Integration: Implement integration with a secrets management solution to securely load and manage your CA certificate. This is crucial for protecting your CA's private key.
  • Observability: Integrate with an observability platform to monitor the health and performance of your Temporal client and server. This helps you detect and resolve issues more quickly.

Conclusion: Successfully Implementing TLS without mTLS

Alright, that was a lot to take in, but let's recap. When you want to set up TLS with your Temporal .NET SDK without mTLS, you need to ensure your SDK trusts the certificate presented by your gateway. The best way to achieve this is by providing the SDK with the CA certificate. This tells the SDK to validate the certificate's authenticity. You should configure the TlsOptions object with the CA certificate, and then, pass these TlsOptions to your TemporalClientOptions during client creation.

Remember that if you're in a testing environment, disabling certificate validation might provide a quick fix, but it should never be used in production. Always prioritize security. Take the time to understand certificate authorities, the steps involved in configuring the SDK to trust a specific CA, and consider the security implications of your decisions.

By following the steps outlined in this article, you should be well on your way to setting up a secure TLS connection between your client, Istio gateway, and Temporal server without the need for mTLS, and you'll avoid that nasty InvalidCertificate(UnknownIssuer) error. Happy coding, and stay secure, guys!