CompletableFuture<OAuth2TokenDescriptor> introspect(String token, String tokenTypeHint) {
        final ClientAuthentication clientAuthentication = clientAuthentication();
        final TokenOperationRequest tokenOperationRequest = TokenOperationRequest.of(clientAuthentication,
                                                                                     token, tokenTypeHint);
        return introspectionEndpoint.execute(tokenOperationRequest);
    }
Implements Token introspection request/response flow, as per
<a href="https://datatracker.ietf.org/doc/html/rfc7662">RFC 7662</a>.
oauth2/src/main/java/com/linecorp/armeria/server/auth/oauth2/TokenIntrospection.java