Resource server examples incorrectly use hyphenated `opaque-token` properties namespace

I just encountered a problem with property overriding when I tried to override the client-id of the opaque-token property of the resourceserver configuration in Spring Security.

In my code I am loading the value as following via an @Value annotation, in one of my configuration classes:

@Value("${spring.security.oauth2.resourceserver.opaque-token.client-id}")

This is in accordance with the documented naming convention for the key as can be seen here:
https://docs.spring.io/spring-security/reference/servlet/oauth2/resource-server/opaque-token.html#oauth2resourceserver-opaque-introspectionuri

Please observe, that both opaque-token and client-id use a hyphen in their name.

If I place the correct value for this key directly into the application.yaml file then everything works as expected. However, I wanted to override this value using the relaxed binding rules for environment variables and used the following variable name:

SPRING_SECURITY_OAUTH2_RESOURCESERVER_OPAQUE_TOKEN_CLIENT_ID

However this did now work, and after some debugging I found that specifically the ReactiveOAuth2ResourceServerOpaqueTokenConfiguration (see https://github.com/spring-projects/spring-boot/blob/main/spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/security/oauth2/resource/reactive/ReactiveOAuth2ResourceServerOpaqueTokenConfiguration.java) was not receiving the overwritten value, and it appears that the reason is, that this class is using a different key format for loading the resource server properties, which is:

@ConditionalOnProperty(name = "spring.security.oauth2.resourceserver.opaquetoken.introspection-uri")

Observe, that there the opaquetoken is not using a hyphen. I then realized, that according to the relaxed binding convention, I should maybe remove the underscores in placed where a hyphen is used and I changed the environment variable name to the following:

SPRING_SECURITY_OAUTH2_RESOURCESERVER_OPAQUETOKEN_CLIENTID

This did not work for two reasons:

1. The client-id was no longer correctly bound, since I removed the underscore also from CLIENT_ID.
2. My own annotation was still using the opaque-token format (with a hyphen).

After some experiments with different placements of underscores and hyphens, I found that the only working configuration for me was the following:

1. In my application.yaml file I had to remove the hyphen from opaque-token and define it as opaquetoken (which is different from the documented format in the link at the top).
2. In my own configuration classes I had to adjust the value annotation and load the client id via @Value("${spring.security.oauth2.resourceserver.opaquetoken.client-id}")
3. I had to change the environment variable and use the following format: SPRING_SECURITY_OAUTH2_RESOURCESERVER_OPAQUETOKEN_CLIENT_ID (not that the OPAQUETOKEN part is without underscore, but the CLIENT_ID part uses an underscore, which strictly speaking is not how the relaxed binding convention for environment variables is documented.

The original reason, why I had to look into this, is because I was being hit by the same error as described in this issue, since the client-id was not correctly configured in my resource server:
https://github.com/spring-projects/spring-security/issues/7858

To Reproduce

1. Configure a resource server with spring security.
2. Define a default opaque-token.client-id in the application.yaml for the resource server
3. Then try to override the client-id of the opaque-token.client-id using an environment variable
4. Observer that the old client-id is being used.

Expected behavior

1. Overriding works correctly
2. Consistent use of opaque-token vs. opaquetoken in documentation and internal implementation.

May I request a clarification on the following items:

1. If the use of opaquetoken over opaque-token in the ReactiveOAuth2ResourceServerOpaqueTokenConfiguration is considered correct.
2. If the recommended format of the relaxed binding environment variable name should be:
   a) SPRING_SECURITY_OAUTH2_RESOURCESERVER_OPAQUETOKEN_CLIENTID or
   b) SPRING_SECURITY_OAUTH2_RESOURCESERVER_OPAQUETOKEN_CLIENT_ID or
   c) SPRING_SECURITY_OAUTH2_RESOURCESERVER_OPAQUE_TOKEN_CLIENT_ID or
   Only b) worked for me.
3. If I should follow the documentation and use opaque-token in the application.yaml or if rather opaquetoken should be used.

Start with spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/security/oauth2/resource/reactive/ReactiveOAuth2ResourceServerOpaqueTokenConfiguration.java and compare its conditional property with the documented opaque-token key. Reproduce the environment-variable override described in the issue and verify that YAML, @Value, and environment-variable naming behave consistently when the correction is complete.