This commit combines security autoconfigurations for
management endpoints and the rest of the application. By default,
if Spring Security is on the classpath, it turns on @EnableWebSecurity.
In the presence of another WebSecurityConfigurerAdapter this backs off
completely. A default AuthenticationManager is also provided with a user
and generated password. This can be turned off by specifying a bean of
type AuthenticationManager, AuthenticationProvider or UserDetailsService.
Closes gh-7958
Phillip Webb
Madhura Bhave
Andy Wilkinson
Dave Syer