Loki basic authentication

Hello.
I’m developing ASP.NET web application. I want to send logs by Serilog to Grafana Loki.
I created new account and got a problem with preinstalled Loki Data Source. The problem is that I don’t know password of created user in Loki Data Source and I can’t reset it (Also I can’t modify config in any ways).
Therefore when I try to log messages via Serilog.Sinks.Grafana.Loki I get unauthorized exception.