Getting active PostgreSQL connection username when stored through authentication configuration in QGIS 3.16

How do I get the username on the current layer PostGIS in QGIS 3.16.2-Hannover?
We tried examples: Getting active PostgreSQL connection username when stored through authentication configuration in QGIS 3, but they don’t work.

When running this script, variable username is empty:

layer = iface.activeLayer()
provider = layer.dataProvider()
username = QgsDataSourceUri(provider.dataSourceUri()).username()
print (username)

This is result of provider.dataSourceUri()):

<QgsDataSourceUri: dbname=’postgres’ host= localhost port=5432
sslmode=disable key=’id’ srid=4326 type=Point
checkPrimaryKeyUnicity=’1′ table="locations"."airlines" (geom)>

The value of the username is missing, the question is how to get the username for the current layer?

SELECT user;