Fix code review issues: remove trailing whitespace and add cert validation

- Removed trailing whitespace from syslog.py and usage.md
- Added warning when only one of certfile_path/keyfile_path is provided
- Improved error handling for incomplete TLS client certificate configuration

Co-authored-by: seanthegeek <44679+seanthegeek@users.noreply.github.com>

docs/source/usage.md

@@ -171,8 +171,8 @@ The full set of configuration options are:
   - `check_timeout` - int: Number of seconds to wait for a IMAP
       IDLE response or the number of seconds until the next
       mail check (Default: `30`)
-  - `since` - str: Search for messages since certain time. (Examples: `5m|3h|2d|1w`) 
-      Acceptable units - {"m":"minutes", "h":"hours", "d":"days", "w":"weeks"}. 
+  - `since` - str: Search for messages since certain time. (Examples: `5m|3h|2d|1w`)
+      Acceptable units - {"m":"minutes", "h":"hours", "d":"days", "w":"weeks"}.
       Defaults to `1d` if incorrect value is provided.
 - `imap`
   - `host` - str: The IMAP server hostname or IP address
@@ -240,7 +240,7 @@ The full set of configuration options are:
     group and use that as the group id.
 
     ```powershell
-    New-ApplicationAccessPolicy -AccessRight RestrictAccess 
+    New-ApplicationAccessPolicy -AccessRight RestrictAccess
     -AppId "<CLIENT_ID>" -PolicyScopeGroupId "<MAILBOX>"
     -Description "Restrict access to dmarc reports mailbox."
     ```
@@ -344,17 +344,17 @@ The full set of configuration options are:
   - `timeout` - float: Connection timeout in seconds for TCP/TLS (Default: `5.0`)
   - `retry_attempts` - int: Number of retry attempts for failed connections (Default: `3`)
   - `retry_delay` - int: Delay in seconds between retry attempts (Default: `5`)
-  
+
   **Example UDP configuration (default):**
-  
+
   ```ini
   [syslog]
   server = syslog.example.com
   port = 514
   ```
-  
+
   **Example TCP configuration:**
-  
+
   ```ini
   [syslog]
   server = syslog.example.com
@@ -363,9 +363,9 @@ The full set of configuration options are:
   timeout = 10.0
   retry_attempts = 5
   ```
-  
+
   **Example TLS configuration with server verification:**
-  
+
   ```ini
   [syslog]
   server = syslog.example.com
@@ -374,9 +374,9 @@ The full set of configuration options are:
   cafile_path = /path/to/ca-cert.pem
   timeout = 10.0
   ```
-  
+
   **Example TLS configuration with mutual authentication:**
-  
+
   ```ini
   [syslog]
   server = syslog.example.com
@@ -394,7 +394,7 @@ The full set of configuration options are:
       credentials, None to disable (Default: `None`)
   - `token_file` - str: Path to save the token file
       (Default: `.token`)
-      
+
     :::{note}
     credentials_file and token_file can be got with [quickstart](https://developers.google.com/gmail/api/quickstart/python).Please change the scope to `https://www.googleapis.com/auth/gmail.modify`.
     :::
@@ -494,7 +494,7 @@ Update the limit to 2k per example:
 PUT _cluster/settings
 {
   "persistent" : {
-    "cluster.max_shards_per_node" : 2000 
+    "cluster.max_shards_per_node" : 2000
   }
 }
 ```

parsedmarc/syslog.py

@@ -52,10 +52,10 @@ class SyslogClient(object):
         self.timeout = timeout
         self.retry_attempts = retry_attempts
         self.retry_delay = retry_delay
-        
+
         self.logger = logging.getLogger("parsedmarc_syslog")
         self.logger.setLevel(logging.INFO)
-        
+
         # Create the appropriate syslog handler based on protocol
         log_handler = self._create_syslog_handler(
             server_name,
@@ -68,7 +68,7 @@ class SyslogClient(object):
             retry_attempts,
             retry_delay,
         )
-        
+
         self.logger.addHandler(log_handler)
 
     def _create_syslog_handler(
@@ -110,24 +110,31 @@ class SyslogClient(object):
                         # TLS protocol
                         # Create SSL context
                         ssl_context = ssl.create_default_context()
-                        
+
                         # Configure server certificate verification
                         if cafile_path:
                             ssl_context.load_verify_locations(cafile=cafile_path)
-                        
+
                         # Configure client certificate authentication
                         if certfile_path and keyfile_path:
                             ssl_context.load_cert_chain(
                                 certfile=certfile_path,
                                 keyfile=keyfile_path,
                             )
-                        
+                        elif certfile_path or keyfile_path:
+                            # Warn if only one of the two required parameters is provided
+                            self.logger.warning(
+                                "Both certfile_path and keyfile_path are required for "
+                                "client certificate authentication. Client authentication "
+                                "will not be used."
+                            )
+
                         # Create TCP handler first
                         handler = logging.handlers.SysLogHandler(
                             address=(server_name, server_port),
                             socktype=socket.SOCK_STREAM,
                         )
-                        
+
                         # Wrap socket with TLS
                         if hasattr(handler, "socket") and handler.socket:
                             handler.socket = ssl_context.wrap_socket(
@@ -135,9 +142,9 @@ class SyslogClient(object):
                                 server_hostname=server_name,
                             )
                             handler.socket.settimeout(timeout)
-                        
+
                         return handler
-                        
+
                 except Exception as e:
                     if attempt < retry_attempts:
                         self.logger.warning(