[funimation] establish session before logging in

Added an initial HTTP GET request with the login URL before attempting
to log in. This allows Funimation to set any session cookies it
requires. This request is necessary for Funimation to render the login
page or to accept login requests.

Fixes #10639

youtube_dl/extractor/funimation.py

@@ -87,26 +87,43 @@ class FunimationIE(InfoExtractor):
         (username, password) = self._get_login_info()
         if username is None:
             return
+
         data = urlencode_postdata({
             'email_field': username,
             'password_field': password,
         })
+
         user_agent = self._extract_cloudflare_session_ua(self._LOGIN_URL)
         if not user_agent:
             user_agent = 'Mozilla/5.0 (Windows NT 5.2; WOW64; rv:42.0) Gecko/20100101 Firefox/42.0'
-        login_request = sanitized_Request(self._LOGIN_URL, data, headers={
+        headers = {
             'User-Agent': user_agent,
             'Content-Type': 'application/x-www-form-urlencoded'
-        })
+        }
+
+        # Request home page to establish initial session and cookies
+        self._download_webpage(
+            self._LOGIN_URL, None,
+            note='Starting session with Funimation',
+            headers=headers)
+
+        # Log in
         login_page = self._download_webpage(
-            login_request, None, 'Logging in as %s' % username)
+            self._LOGIN_URL, None,
+            data=data,
+            note='Logging in as %s' % username,
+            headers=headers)
+
+        # Check for successful login
         if any(p in login_page for p in ('funimation.com/logout', '>Log Out<')):
             return
+
         error = self._html_search_regex(
             r'(?s)<div[^>]+id=["\']errorMessages["\'][^>]*>(.+?)</div>',
             login_page, 'error messages', default=None)
         if error:
             raise ExtractorError('Unable to login: %s' % error, expected=True)
+
         raise ExtractorError('Unable to log in')
 
     def _real_initialize(self):