SAML login_hint for Idp routing not documented

We have IDP routing configured for use with login.microsoftonline.com We want to sent the login_hint parameter to Microsoft.

This documentation mentions “loginhint”
https://developer.okta.com/docs/concepts/saml/

But then says to refer to the deep link documentation:
https://developer.okta.com/docs/reference/api/idps/#redirect-with-saml-deep-links

But the deep link documentation does not specify how to include the login hint with idp routing.

When using the signon widget with idp discovery, I can see LoginHint passed as a form field in the POST to the Microsoft Idp, but microsoft expects the form field to be login_hint.

Can someone tell me how we can pass the login_hint parameter on to Microsoft’s Idp?

We are looking to do the same thing and I also noticed that there was missing documentation too. We are using the login hint to skip Okta sign in but it’s not populating in our IdP (Ping). In this case the login hint is not being sent to the IdP in the SAML request so it would be great to get some help on the configuration we will need to add for this to be possible.