Spring security: allow a few pages to be displayed in iframe - spring-mvc

Question

I support a website that uses Spring Security (5.3.3.RELEASE). The site can't be displayed in iframe in other sites because of the following configuration
<security:headers>
<security:frame-options policy="SAMEORIGIN"/>
</security:headers>
Now I am asked to allow a few pages to be displayed in iframe in ANY other sites (not a specific list of sites). I looked at the Spring documentation, and it appears that I can add a bean in the following way:
<security:headers>
<security:frame-options policy="SAMEORIGIN" ref="bean_id"/>
</security:headers>
I am not able to find info about what interface or methods the bean (bean_id) must implement or whether it can be used to decide what pages are frameable. Any help or example is really appreciated.

Answer 1

The interface is of type AllowFromStrategy. But that interface is deprecated since the ALLOW-FROM is an obsolete directive that no longer works in modern browsers, see here. The alternative is to use CSP: frame-ancestors.
Spring Security has support for the Content-Security-Policy header. You can rely on the DelegatingRequestMatcherHeaderWriter implementation to add the headers only to specific pages, like so:
<http>
<!-- ... -->
<headers>
<header ref="headerWriter"/>
</headers>
</http>
<beans:bean id="headerWriter"
class="org.springframework.security.web.header.writers.DelegatingRequestMatcherHeaderWriter">
<beans:constructor-arg>
<bean class="org.springframework.security.web.util.matcher.AntPathRequestMatcher"
c:pattern="/page-with-csp"/>
</beans:constructor-arg>
<beans:constructor-arg>
<beans:bean
class="org.springframework.security.web.header.writers.ContentSecurityPolicyHeaderWriter"/>
</beans:constructor-arg>
</beans:bean>