The primer system automatically follows the HTTP redirects
301 Moved Permanently and
302 Found. Sometimes login systems
produce additional links that must be followed to get the login cookie, but
document.location or a page that simply says "click here to continue".
The special Custom Primer URL token
!FOLLOW_LINK can be used instead of a
URL to follow the first link generated by the previous primer's fetch. This can
be added multiple times to follow multiple links.