Current user map entries can be listed with

GET 'https://127.0.0.1:8096/api/v8/connector/configurations/user-map'  
{
    "payloadType": "ConfigurationItemsPayload",
    "payloadVersion": "1",
    "payload": [
        {
            "item": "app_user",
            "currentValue": "% europe europe"
        }
    ]
}

In order to create a user in memory, the password and data service name will have to be passed in a payload:

PUT 'https://127.0.0.1:8096/api/v2/connector/configurations/user-map/items/newusername' \
--header 'Content-Type: application/json' \
--header 'Authorization: ••••••' \
--data '{ 
  "value" : "password data-service [optional affinity]" 
}'

Note that after this call, the user map only exists in memory. Persistent storage to disk will need to be done as follows:

PUT 'https://127.0.0.1:8096/api/v8/connector/configurations/user-map/items/write-to-disk' \
--header 'Content-Type: application/json' \
--header 'Authorization: ••••••' \
--data '{ 
  "value" : "true" 
}'