umqtt.simple: Add MQTT user/password authentication.

Limitation the total length of client id, user name and password must
be under 111 characters.

umqtt.simple/umqtt/simple.py

@@ -7,7 +7,7 @@ class MQTTException(Exception):
 
 class MQTTClient:
 
-    def __init__(self, client_id, server, port=0, ssl=False):
+    def __init__(self, client_id, server, port=0, user=None, password=None, ssl=False):
         if port == 0:
             port = 8883 if ssl else 1883
         self.client_id = client_id
@@ -16,6 +16,8 @@ class MQTTClient:
         self.ssl = ssl
         self.pid = 0
         self.cb = None
+        self.user = user
+        self.pswd = password
 
     def _send_str(self, s):
         self.sock.write(struct.pack("!H", len(s)))
@@ -43,9 +45,15 @@ class MQTTClient:
         msg = bytearray(b"\x10\0\0\x04MQTT\x04\x02\0\0")
         msg[1] = 10 + 2 + len(self.client_id)
         msg[9] = clean_session << 1
+        if self.user is not None:
+            msg[1] += 2 + len(self.user) + 2 + len(self.pswd)
+            msg[9] |= 0xC0
         self.sock.write(msg)
         #print(hex(len(msg)), hexlify(msg, ":"))
         self._send_str(self.client_id)
+        if self.user is not None:
+            self._send_str(self.user)
+            self._send_str(self.pswd)
         resp = self.sock.read(4)
         assert resp[0] == 0x20 and resp[1] == 0x02
         if resp[3] != 0: