How to set User and Password in the broker

[ericoud]

Hello, I didn't find a way to set the user name and the password in the broker side. My clients must use user and password for authentication. I was using picoMQTT but there is no retain feature (but authentication can be set).
In the help there is an information about credential :
<libraries/TinyMqtt/src/my_credentials.h> (wifi setup)
But the file doesn't exist, and I am not sure it is for the broker.
does authetication is available on tinyMQTT?