ldap: encode string before using urlparse.quote() on them (#31273)

quote() only handle byte strings or ASCII only unicode strings with Python3,
to be compatible with both python versions the best is to encode string before
quoting them.

src/authentic2/backends/ldap_backend.py

@@ -977,20 +977,19 @@ class LDAPBackend(object):
         '''Build the exernal id for the user, use attribute that eventually
            never change like GUID or UUID.
         '''
-        l = []
+        parts = []
         for attribute in external_id_tuple:
             quote = True
             if ':' in attribute:
                 attribute, param = attribute.split(':')
                 quote = 'noquote' not in param.split(',')
-            v = attributes[attribute]
-            if isinstance(v, list):
-                v = v[0]
-            v = force_text(v)
+            part = attributes[attribute]
+            if isinstance(part, list):
+                part = part[0]
             if quote:
-                v = urlparse.quote(v)
-            l.append(v)
-        return ' '.join(v for v in l)
+                part = urlparse.quote(part.encode('utf-8'))
+            parts.append(part)
+        return ' '.join(part for part in parts)
 
     def lookup_by_username(self, username):
         User = get_user_model()