The way to use Moodle as Identity Provider is to use its database as the authentication source of the Identity Provider.
An open source solution is to install and deploy simpleSAMLphp as Identity Provider.
The use the sqlauth:sql authsource connecting it to Moodle, or implement an specific auth module.
If you have some budget for that project, I can take care of all the process. (BTW. I'm the author of the auth_saml module.)
Authentication
Moodle as SAML Identity Provider
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