Oak Signed Cookies error

Hi!
I keeping getting this error:

error: Uncaught (in promise) TypeError: keys required for signed cookies.
        throw new TypeError("keys required for signed cookies.");

error: Uncaught (in promise) TypeError: keys required for signed cookies.
        throw new TypeError("keys required for signed cookies.");

I tried searching for how to use a cookie secret, but I couldn't find it.

This is the line where it fails:

ctx.cookies.set("clientState", "random-string", { maxAge: 1000 * 60 * 5, signed: true })

ctx.cookies.set("clientState", "random-string", { maxAge: 1000 * 60 * 5, signed: true })