As per the title. I want users who have an account on my WordPress website, to use their credentials to log in to other services. So, instead of logging into my site with, say Google, I want to set up my website such that my users can login to a third party website with their credentials for my website.

I suppose I could write all the necessary code myself, but, surely, this has been done, and is used?

Any examples or plugins that provide this feature?