SiYuan 2.9.0-3.8.6 - Unauthenticated XSS via check-auth "to" Parameter

SiYuan 2.9.0 through 3.8.6 serves the unauthenticated /check-auth authorization page app/stage/auth.html with a script that assigns the to query parameter to window.location.href without scheme validation. A crafted link whose to value is a javascript: URI executes script in the kernel origin onc...