Offboarding external collaborators

Has anyone been looking into management of external collaborators in regards to offboarding? We have SAML auth. against our Azure AD and 98% will gain access to our aganization via Azure AD. However we do have external vendors and really want to be able to invite these adhoc into specific repo’s as external collaborators and this works really great and effortless. However offboarding these users and the general lifecycle og managing external collaborators seems a bit thin.

So anyone aware of any workflows og apps helping with offboarding extenal collaborators? One idea could be to exclude external user if no logon or commit activity has been detected within x days?

Any experience or input is greatly appreciated!