diff --git a/README.md b/README.md
index d1860ad..1494dab 100644
--- a/README.md
+++ b/README.md
@@ -41,6 +41,15 @@ uas(block=False)  # returns a `pysipp.launch.PopenRunner` instance by default
 uac()  # run client synchronously
 ```
 
+## Authentication
+When using the `[authentication]` [sipp keyword](https://sipp.readthedocs.io/en/latest/scenarios/keywords.html#authentication)
+in scenarios, providing the credentials can be done with the
+`auth_username` and `auth_password` arguments, for example:
+
+```python
+pysipp.client(auth_username='sipp', auth_password='sipp-pass')
+```
+
 ## Multiple Agents
 For multi-UA orchestrations we can use a `pysipp.scenario`.
 The scenario from above is the default agent configuration:
diff --git a/pysipp/command.py b/pysipp/command.py
index 417bc6e..6b87066 100644
--- a/pysipp/command.py
+++ b/pysipp/command.py
@@ -212,6 +212,7 @@ def todict(self):
     # SIP vars
     '-cid_str {cid_str} ',
     '-base_cseq {base_cseq} ',
+    '-au {auth_username} ',
     '-ap {auth_password} ',
     # load settings
     '-r {rate} ',