admin/extensions: SAML private key passphrase addition

Passphrase for SAML private key to prevent that
site name changes result in metadata change
(Bug #1829108).

(cherry picked from commit 915c4f34)
(cherry picked from commit db959508)

source/administration/extensions.rst

@@ -564,6 +564,12 @@ If you wish to use :ref:`SAML authentication <saml>` anywhere on your site, you
    .. warning::
       The SHA1 algorithm is only provided for backwards compatibility. Unless you absolutely must use it, it is recommended to avoid it and use at least SHA256 instead.
 
+#. **Private key passphrase**: :index:`For <single: SAML; Private key passphrase for SAML authentication>` added security, enter a passphrase to protect the private key.
+
+   .. note::
+      This passphrase now allows you to change your site name without that impacting the SAML certificate.
+
+#. **New private key passphrase**: If you want to change the private key passphrase, you can do so here.
 #. **Public key**: The public key is generated and rotated automatically. Typically, you would not need to copy it from here since you copy the entire metadata. It is displayed for verification purposes.
 #. Click the *Create new key / certificate* button if you want to force the creation of a new public key.
 #. Click the *Save* button to make your changes.