Add hasScope as a valid SpEL expression to PreAuthorize

[ngocnhan-tran1996]

Closes: gh-18013

[jzheaux]

Hi, @ngocnhan-tran1996. We want to be careful about adding to the expression root, especially now that it has implications for AuthorizationManagerFactory. Alternatively, we could consider an interface OAuth2AuthorizationManagerFactory like this:

public interface OAuth2AuthorizationManagerFactory<T> {
    default AuthorizationManager<T> hasScope(String scope) {
        return OAuth2AuthorizationManagers.hasScope(scope);
    }

    // ...
}

And a default implementation:

@Bean 
OAuth2AuthorizationManagerFactory<Object> oauth2() {
    return new DefaultOAuth2AuthorizationManagerFactory();
}

That takes an AuthorizationManagerFactory as a parameter in support of MFA:

@Bean 
OAuth2AuthorizationManagerFactory<Object> oauth2(AuthorizationManagerFactory<Object> mfa) {
    return new OAuth2AuthorizationManagerFactory(mfa);
}

And then do:

@PreAuthorize("@oauth2.hasScope('message:read')")

I like this pattern since it allows for other modules to add their own expressions as well, without needing to change or extend SecurityExpressionRoot.

[ngocnhan-tran1996]

@jzheaux

I’ve made the requested changes. Let me know if anything else is needed.