SAML_IDP_SP_FIELD_DEFAULT_PROCESSOR env does not work

[Crazy0416]

According to the this document, the SAML_IDP_SP_FIELD_DEFAULT_PROCESSOR value is a value that can set the default processor, so I applied it to the code, but the default value has not changed.
I checked the cause and the most recent version 0.7.2 was released in 2020, but the code setting that default value seems to have been committed in 2021.
I think we should release a new version or update the document.