Question about stored credentials and authentication -> changing username values after user input

Hello all

I built a custom connector to format api data into tables. I am using basic authentication and I need to be able to prepend a hard-coded string to the username of whatever is stored in the credentials before it is used for any request. There is barely a couple sentences for basic auth on the documentation so I was hoping someone on here could shed some light on this for me.

Here is what I have for the auth at the moment:

CustomConnector = [
TestConnection = (dataSourcePath as text) => { "CustomConnector.Contents", dataSourcePath},
Authentication = [

UsernamePassword = [ ]

],
Label = "CustomConnector"
];

Thanks in advance