You cannot add field to Content type. After clicking Add field definition message The CSRF token is invalid. Please try to resubmit the form. appears. Refreshing and relogging doesn't help.

Steps:

1. Go to Admin > Content Types > Content
2. Click Edit button right to Article
3. Click Add field definition

Actual result:

The CSRF token is invalid. Please try to resubmit the form.

Expected result:

New field definition appears in form.