F5 iControl REST Unauthenticated SSRF Token Generation RCE

This module exploits a pre-auth SSRF in the F5 iControl REST API's
/mgmt/shared/authn/login endpoint to generate an X-F5-Auth-Token that
can be used to execute root commands on an affected BIG-IP or BIG-IQ
device. This vulnerability is known as CVE-2021-22986.

CVE-2021-22986 affects the following BIG-IP versions:

* 12.1.0 - 12.1.5
* 13.1.0 - 13.1.3
* 14.1.0 - 14.1.3
* 15.1.0 - 15.1.2
* 16.0.0 - 16.0.1

And the following BIG-IQ versions:

* 6.0.0 - 6.1.0
* 7.0.0
* 7.1.0

Tested against BIG-IP Virtual Edition 16.0.1 in VMware Fusion.