Strange credentials validation behaviour

I’m facing very strange behavior with php SDK while connecting to a single node couchbase cluster.

<?php $connectionString = "couchbase://"; $options = new \Couchbase\ClusterOptions(); $options->credentials('usr', 'pass'); $cluster = new \Couchbase\Cluster($connectionString, $options); // get a bucket reference $bucket = $cluster->bucket("db_test"); // get a collection reference $collection = $bucket->defaultCollection(); $document = ["player_id" => "1", "player_name" => "Ziko", "player_dob" => "1985-12-20"]; $res = $collection->upsert("player_id:7", $document);

The above script works just fine. After running the above script for the first time, I can modify the the password string or event set it to an empty string, yet the upsert operation is successfully completed!
Any explanations ?