Where should I start?
Create a simplest spring boot resource owner password grant authorization server.
Using generated security password: 5ba14387-84fb-458a-a301-9a1993f79b55. What is it?
When there is no UserDetail beans, spring (UserDetailsServiceAutoConfiguration) generate a sample username=user, password=<randompassword>.
It's not the clientSecret, it's end user password can be used in Resource Owner Grant password