[MM-10346] CSRF Token Implementation + Tests (#10067)

* CSRF Token Implementation + Tests

Remove debug statements

Implement requested changes

* Fix non-cookie authentication methods stripping auth data from requests

* Fail when CSRF cookie is not returned as part of login

config/default.json

@@ -74,7 +74,8 @@
         "EnableAPITeamDeletion": false,
         "ExperimentalEnableHardenedMode": false,
         "EnableEmailInvitations": false,
-        "ExperimentalLdapGroupSync": false
+        "ExperimentalLdapGroupSync": false,
+        "ExperimentalStrictCSRFEnforcement": false
     },
     "TeamSettings": {
         "SiteName": "Mattermost",