Is it possible to turn on table of contents for all pages ?

[sappy]

I try to find a way to set the table of contents ( TOC ) be True by default.
I know that set the front matter can turn on TOC, but I want to find a way to config this parameter in config.toml for all pages.
The code show me that you check .Params.toc first, and determine to show the TOC or not.
To my knowledge, Hugo's config.toml variable is .Site.Params.toc, and I don't know how to set .Params.toc in config.toml.
Is it possible to turn on the table of contents in config.toml for all pages?
Thanks for your great theme.