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Working with certificates

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Working with certificates

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If you’ve enabled SSL on Elasticsearch with X-Pack or through a proxy in front of Elasticsearch, and the Certificate Authority (CA) that generated the certificate is trusted by the machine running the client code, there should be nothing you’ll have to do to talk to the cluster over HTTPS with the client.

If you are using your own CA which is not trusted however, .NET won’t allow you to make HTTPS calls to that endpoint by default. With .NET, you can pre-empt this though a custom validation callback on the global static ServicePointManager.ServerCertificateValidationCallback. Most examples you will find doing this this will simply return true from the validation callback and merrily whistle off into the sunset. This is not advisable as it allows any HTTPS traffic through in the current AppDomain without any validation. Here’s a concrete example:

Imagine you deploy a web application that talks to Elasticsearch over HTTPS through NEST, and also uses some third party SOAP/WSDL endpoint; by setting

ServicePointManager.ServerCertificateValidationCallback +=
(sender, cert, chain, errors) => true

validation will not be performed for HTTPS connections to both Elasticsearch and that external web service.

Validation configuration

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It’s possible to also set a callback per service endpoint with .NET, and both Elasticsearch.NET and NEST expose this through connection settings (ConnectionConfiguration with Elasticsearch.Net and ConnectionSettings with NEST). You can do your own validation in that handler or use one of the baked in handlers that we ship with out of the box, on the static class CertificateValidations.

The two most basic ones are AllowAll and DenyAll, which accept or deny all SSL traffic to our nodes, respectively. Here’s a couple of examples.

Denying all certificate validation

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Here we set up ConnectionSettings with a validation callback that denies all certificate validation

public class DenyAllCertificatesCluster : SslAndKpiXPackCluster
{
    protected override ConnectionSettings ConnectionSettings(ConnectionSettings s) => s
        .ServerCertificateValidationCallback((o, certificate, chain, errors) => false)
        .ServerCertificateValidationCallback(CertificateValidations.DenyAll); 
}

synonymous with the previous lambda expression

Allowing all certificate validation

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Here we set up ConnectionSettings with a validation callback that allows all certificate validation

public class AllowAllCertificatesCluster : SslAndKpiXPackCluster
{
    protected override ConnectionSettings ConnectionSettings(ConnectionSettings s) => s
        .ServerCertificateValidationCallback((o, certificate, chain, errors) => true)
        .ServerCertificateValidationCallback(CertificateValidations.AllowAll); 
}

synonymous with the previous lambda expression

Allowing certificates from a Certificate Authority

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If your client application has access to the public CA certificate locally, Elasticsearch.NET and NEST ship with some handy helpers that can assert that a certificate the server presents is one that came from the local CA.

If you use X-Pack’s certgen tool to generate SSL certificates, the generated node certificate does not include the CA in the certificate chain, in order to cut down on SSL handshake size. In those case you can use CertificateValidations.AuthorityIsRoot and pass it your local copy of the CA public key to assert that the certificate the server presented was generated using it

public class CertgenCaCluster : SslAndKpiXPackCluster
{
    public CertgenCaCluster() : this(new SslAndKpiClusterConfiguration()) { }
    public CertgenCaCluster(SslAndKpiClusterConfiguration configuration) : base(configuration) { }
    protected override ConnectionSettings ConnectionSettings(ConnectionSettings s) => s
        .ServerCertificateValidationCallback(
            CertificateValidations.AuthorityIsRoot(new X509Certificate(this.ClusterConfiguration.FileSystem.CaCertificate))
        );
}

If your local copy does not match the server’s CA, the client will fail to connect

public class BadCertgenCaCluster : SslAndKpiXPackCluster
{
    protected override ConnectionSettings ConnectionSettings(ConnectionSettings s) => s
        .ServerCertificateValidationCallback(
            CertificateValidations.AuthorityPartOfChain(new X509Certificate(this.ClusterConfiguration.FileSystem.UnusedCaCertificate))
        );
}

If you go for a vendor generated SSL certificate, it’s common practice for the certificate to include the CA and any intermediary CAs in the certificate chain. When using such a certificate, use CertificateValidations.AuthorityPartOfChain which validates that the local CA certificate is part of the chain that was used to generate the server’s key.

Client Certificates

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X-Pack also allows you to configure a PKI realm to enable user authentication through client certificates. The certgen tool included with X-Pack allows you to generate client certificates as well and assign the distinguished name (DN) of the certificate to a user with a certain role.

certgen by default only generates a public certificate (.cer) and a private key .key. To authenticate with client certificates, you need to present both as one certificate. The easiest way to do this is to generate a pfx or p12 file from the .cer and .key and attach these to requests using new X509Certificate(pathToPfx).

If you do not have a way to run openssl or Pvk2Pfx to do this as part of your deployments the clients ships with a handy helper to generate one on the fly by passing the paths to the .cer and .key files that certgen outputs. Sadly, this functonality is not available on .NET Core because the PublicKey property cannot be set on the crypto service provider that is used to generate the pfx file at runtime.

You can set Client Certificates to use on all connections on ConnectionSettings

public class PkiCluster : CertgenCaCluster
{
    public PkiCluster() : base(new SslAndKpiClusterConfiguration
    {
        DefaultNodeSettings =
        {
            {"xpack.security.authc.realms.file1.enabled", "false"},
            {"xpack.security.http.ssl.client_authentication", "required"}
        }
    }) { }

    protected override ConnectionSettings Authenticate(ConnectionSettings s) => s 
        .ClientCertificate(
            Elasticsearch.Net.ClientCertificate.LoadWithPrivateKey(
                this.ClusterConfiguration.FileSystem.ClientCertificate, 
                this.ClusterConfiguration.FileSystem.ClientPrivateKey, 
                "") 
        );
}

	Set the client certificate on `ConnectionSettings`
	The path to the `.cer` file
	The path to the `.key` file
	The password for the private key

Or per request on RequestConfiguration which will take precedence over the ones defined on ConnectionConfiguration

Object Initializer syntax example

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new RootNodeInfoRequest
{
    RequestConfiguration = new RequestConfiguration
    {
        ClientCertificates = new X509Certificate2Collection { new X509Certificate2(this.Certificate) }
    }
}

Fluent DSL example

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s => s
.RequestConfiguration(r => r
        .ClientCertificate(this.Certificate)
)

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