If configured, Elastic Stack will sign outgoing SAML messages.

As a prerequisite, you need to generate a signing key and a self-signed certificate. You need to share this certificate with your SAML Identity Provider so that it can verify the received messages. The key needs to be unencrypted. The exact procedure is system dependent, you can use for example openssl

openssl req -new -x509 -days 3650 -nodes -sha256 -out saml-sign.crt -keyout saml-sign.key

Place the files under the saml folder and add them to the existing SAML bundle, or create a new one as described earlier.

In our example, the certificate and the key will be located in the path /app/config/saml/saml-sign.{crt,key}:

$ tree .
.
└── saml
    ├── saml-sign.crt
    └── saml-sign.key

Make sure that the bundle is included with your deployment.

Adjust your realm configuration accordingly:

    signing.certificate: /app/config/saml/saml-sign.crt 
    signing.key: /app/config/saml/saml-sign.key 

When configured with a signing key and certificate, Elastic Stack will sign all outgoing messages (SAML Authentication Requests, SAML Logout Requests, SAML Logout Responses) by default. This behavior can be altered by configuring signing.saml_messages appropriately with the comma separated list of messages to sign. Supported values are AuthnRequest, LogoutRequest and LogoutResponse and the default value is *.

For example:

xpack:
  security:
    authc:
      realms:
        saml-realm-name:
          order: 2
          ...
          signing.saml_messages: AuthnRequest 
          ...