diff --git a/cylc/flow/network/client.py b/cylc/flow/network/client.py
index 27798c58741..b2cec410f56 100644
--- a/cylc/flow/network/client.py
+++ b/cylc/flow/network/client.py
@@ -20,6 +20,7 @@
     abstractmethod,
 )
 import asyncio
+import getpass
 import os
 from shutil import which
 import socket
@@ -366,6 +367,16 @@ def get_header(self) -> dict:
 
             if cmd.startswith(cylc_bin_dir):
                 cmd = cmd.replace(cylc_bin_dir, '')
+        try:
+            behalf_of = f" (possibly on behalf of {os.getlogin()})"
+        except OSError:
+            behalf_of = None
+        if not behalf_of:
+            try:
+                behalf_of = f" (possibly on behalf of {getpass.getuser()})"
+            except OSError:
+                behalf_of = ''
+
         return {
             'meta': {
                 'prog': cmd,
@@ -374,6 +385,7 @@ def get_header(self) -> dict:
                     os.getenv(
                         "CLIENT_COMMS_METH",
                         default=CommsMeth.ZMQ.value
-                    )
+                    ),
+                'behalf_of': behalf_of
             }
         }
diff --git a/cylc/flow/network/resolvers.py b/cylc/flow/network/resolvers.py
index 48ef39795ec..60a9beeb524 100644
--- a/cylc/flow/network/resolvers.py
+++ b/cylc/flow/network/resolvers.py
@@ -723,13 +723,14 @@ async def _mutation_mapper(
         Others go to the scheduler command queue.
 
         """
+        behalf_of = meta.get('behalf_of', '')
         user = meta.get('auth_user', self.schd.owner)
         if user == self.schd.owner:
-            log_user = ""  # don't log user name if owner
+            log_user = f" from {self.schd.owner}"
         else:
             log_user = f" from {user}"
 
-        log1 = f'Command "{command}" received{log_user}.'
+        log1 = f'Command "{command}" received{log_user}{behalf_of}.'
         log2 = (
             f"{command}("
             + ", ".join(
diff --git a/tests/integration/network/test_resolvers.py b/tests/integration/network/test_resolvers.py
index 251d01e0ac4..68f5dd2c7c8 100644
--- a/tests/integration/network/test_resolvers.py
+++ b/tests/integration/network/test_resolvers.py
@@ -244,12 +244,19 @@ async def test_command_logging(mock_flow, caplog, log_filter):
     }
     meta["auth_user"] = mock_flow.owner
     await mock_flow.resolvers._mutation_mapper("put_messages", kwargs, meta)
-    assert not log_filter(contains='Command "put_messages" received:')
+    assert not log_filter(
+        contains=f'Command "put_messages" received from {mock_flow.owner}')
 
     meta["auth_user"] = "Dr Spock"
     await mock_flow.resolvers._mutation_mapper("put_messages", kwargs, meta)
     assert log_filter(contains='Command "put_messages" received from Dr Spock')
 
+    meta["auth_user"] = "Dr Spock"
+    meta["behalf_of"] = " (possibly on behalf of Mr Nimoy)"
+    await mock_flow.resolvers._mutation_mapper("put_messages", kwargs, meta)
+    assert log_filter(
+        contains='received from Dr Spock (possibly on behalf of Mr Nimoy)')
+
 
 async def test_command_validation_failure(
     mock_flow,