This. It is very comfortable to use Google OAuth sign in, even if you have a custom domain, but I've run into a few services that will not let you log on with u

This. It is very comfortable to use Google OAuth sign in, even if you have a custom domain, but I've run into a few services that will not let you log on with user/password if you created the account via Single Sign On with Google, regardless if you use the same email.