Easiest IDP to provide out-of-box with SAML2 SP

I am migrating a webapp that currently uses spring-security with basic authentication to use SAML2 SSO.

By default the project provides the embedded LDAP server provided by spring-security-samples-ldap. It allows deployments to replace this LDAP with another LDAP server of their choice.

As the project migrates to use SAML2 SSO as its default authentication mechanism, what would be the easiest SAML2 IDP that can be embedded with the project as the default IDP out-of-the-box.

Thanks for your help.