[API_13] Password authentication not working

[rmartev]

I'm using version 13.0 of the java client API and currently I'm unable to authenticate. Here is a snippet of my code:

RundeckClientBuilder clientBuilder = RundeckClient.builder();
clientBuilder.url("http://localhost:4440");
clientBuilder.login(username, password);
RundeckClient client = clientBuilder.build();
client.testAuth();

The following exception is thrown:
org.rundeck.api.RundeckApiException$RundeckApiLoginException: Login failed for user admin
at org.rundeck.api.ApiCall.login(ApiCall.java:667)
at org.rundeck.api.ApiCall.testLoginAuth(ApiCall.java:137)
at org.rundeck.api.ApiCall.testAuth(ApiCall.java:122)
at org.rundeck.api.RundeckClient.testAuth(RundeckClient.java:267)

Am I using the client the wrong way? Please, hep