This Keystore is automatically created if you do not configure encryption, the Pac4j needs a key to work even though you do not use encryption. So in general if you do not use sign or encryption in the SAML messages (not related to TLS) you do need to configure anything this file will be used only to make the library work, but your IdP will not request your certificate. If you use encryption, you should configure your own Keystore and manage the keys in there.
In the Documentation of the plugin you can found how to configure encryption and how this Keystore works.
Encryption - If your provider requires encryption or signing, you can specify the keystore details here that should be used. If you do not specify a keystore, the plugin would create one with a key that is valid for a year, this key would be recreate when it expires, by default the key is not exposed in the SP metadata if you do not enable signing.
- Keystore path - The path to the keystore file created with the keygen command.
- Key Alias - The alias used in the -alias argument of the keytool< command.
- Keystore password - The password used in the -storepass argument of the keytool command.
- Private Key password - The password used in the -keypass argument of keytool.
- Auth Request Signature - Enable signature of the Redirect Binding Auth Request, If you enable it the encryption and signing key would available in the SP metadata file and URL (JENKINS_URL/securityRealm/metadata). The disable of signing auth request does not work with HTTP redirection binging, it only works for POST binding.