Unfortunately, we have no other choice to flip the ignoreUnknownFields
attribute of `SecurityProperties` has many different target are now set
for that namespace outside the class. See gh-3445 for a potential way
to improve that.
Closes gh-3327
User can enable OAuth2 SSO by declaring the intent (@EnableOAuth2Sso)
and also configuring the client properties (spring.oauth2.client.*).
The spring.oauth2.sso.* are only needed to change the path for the
login (defaults to /login) - any other security configuration for the
protected resources can be added in a WebSecurityConfigurerAdapter
which carries the @EnableOAuth2Sso annotation.
