Add OPAProperties to structure properties

[ali-jalaal]

Expected behaviour

Externalize OPA-related properties using configuration properties to improve configurability.

Actual behaviour

We have some properties such as opaURL, opaPath, and reasonKey. Currently, these properties can only be set through code. Moreover, there are some constants which can be defined as properties.

How to improve

By externalizing these properties using a @ConfigurationProperties (link1, link2), we could:

• manage these properties as a Spring bean
• setting default values
• standardize their name
• validate them
• enable client applications to change them through properties/yaml file, environment variables, system properties, ... without rebuilding code

We could define OPAProperties class:

...
@ConfigurationProperties(prefix = "opa")
@Data
@NoArgsConstructor
public class OpaProperties {
    private String url = "http://localhost:8181";
    private String path;
    private String reasonKey = "en";
    private String requestContextType = "http";
    private String requestContextSubjectType = "java_authentication";
    private String requestResourceType = "endpoint";
    ...
}

and use these properties in classes like OPAAuthorizationManager. (request... properties can also be wrapped in a separate object.)

On the flip side, client applications can easily define and change these properties, for instance in:

• application.yaml:

opa:
  url: http://localhost:8181
  path: tickets/main
  reason-key: de
  ...

• command-line arguments (system properties):

java -jar myapp.jar --opa.url=http://localhost:8181 --opa.path=tickets/main

• environment variables:

export OPA_URL=http://localhost:8181
export OPA_PATH=tickets/main

java -jar myapp.jar

[chendrix]

This was actually on our internal roadmap and we never got to it, so this also looks good to me.