Fix TP-Link Archer C7 long passwords (#3225)

* Fix tplink C7 long passwords

Fixes an issue where passwords longer than 15 chars could not log in to Archer C7 routers.

* Truncate in correct place

* Add comment about TP-Link C7 pass truncation

* Fix lint error

* Truncate comment at 79 chars not 80

homeassistant/components/device_tracker/tplink.py

@@ -277,8 +277,10 @@ class Tplink4DeviceScanner(TplinkDeviceScanner):
         _LOGGER.info("Retrieving auth tokens...")
         url = 'http://{}/userRpm/LoginRpm.htm?Save=Save'.format(self.host)
 
-        # Generate md5 hash of password
-        password = hashlib.md5(self.password.encode('utf')).hexdigest()
+        # Generate md5 hash of password. The C7 appears to use the first 15
+        # characters of the password only, so we truncate to remove additional
+        # characters from being hashed.
+        password = hashlib.md5(self.password.encode('utf')[:15]).hexdigest()
         credentials = '{}:{}'.format(self.username, password).encode('utf')
 
         # Encode the credentials to be sent as a cookie.