This is very necessary in the WordPress ecosystem, as there aren’t many plugins that do this well. FluentAuth is one such plugin, but the problem is that it works as an SSO plugin to log in to WordPress with a user account from other sites, like Facebook for example, but it can’t use the user account from your WordPress account to log in to other places. MiniOrange is one such plugin that allows you to turn WordPress into a server that will authenticate for other sites, but the service is too expensive and their UI/UX is from 1999.