According to the OAuth spec
https://datatracker.ietf.org/doc/html/rfc6749#section-6 when "Refreshing
an Access Token"
> The authorization server MUST ... require client authentication for
confidential clients
Fixes#21418
Co-authored-by: Gusted <williamzijl7@hotmail.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>