Server: Fix requestor e-mail validation

* No longer silently accept pattern 'a@b@c', otherwise stay compatibile.
* Valid patterns are: 'user@fqdn', '<user@fqdn>', 'user <user@fqdn>',
  'user surname <user@fqdn>', no Unicode support, multiple e-mails
  separated by comma are allowed.
* Replace email.utils.parseaddr() with extended regular expression.
* Remove import email.utils as no other users exist.

Signed-off-by: Pavel Kácha <ph@cesnet.cz>

warden3/warden_server/warden_server.py

@@ -14,7 +14,6 @@ import logging
 import logging.handlers
 import json
 import re
-import email.utils
 from traceback import format_tb
 from collections import namedtuple
 from time import sleep
@@ -1466,9 +1465,8 @@ def modify_client(**kwargs):
         return allowed.match(nsid)
 
     def isValidEmail(mail):
-        mails = (email.utils.parseaddr(m) for m in mail.split(","))
-        allowed = re.compile(r"^[a-zA-Z0-9_.%!+-]+@[a-zA-Z0-9-.]+$")  # just basic check
-        valid = (allowed.match(ms[1]) for ms in mails)
+        allowed = re.compile(r"(^[a-zA-Z0-9_ .%!+-]*(?=<.*>))?(^|(<(?=.*(>))))[a-zA-Z0-9_.%!+-]+@[a-zA-Z0-9-.]+\4?$")   # just basic check
+        valid = (allowed.match(ms.strip())for ms in mail.split(','))
         return all(valid)
 
     def isValidID(id):