public OAuth2TokenIntrospectionAuthorizerBuilder realm(String realm) {
        this.realm = requireNonNull(realm, "realm");
        return this;
    }
An HTTP Realm - a name designating of the protected area. OPTIONAL.
oauth2/src/main/java/com/linecorp/armeria/server/auth/oauth2/OAuth2TokenIntrospectionAuthorizerBuilder.java