Log the username of CLI users

This passes the discovered CLI user, if available, and adds them with a
reference to who it might be. Uses getlogin by default, which grabs the
user based on the controlling terminal and if that fails uses getuser
which pulls from environment variables.

This passed couched in the terms of "possibly on behalf of" as this is
data from the client and so is not reliable.

Author: psa

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
             }
         }

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 = 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(

tests/integration/network/test_resolvers.py

@@ -251,6 +251,12 @@ async def test_command_logging(mock_flow, caplog, log_filter):
     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"] = "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,