Github user alopresto commented on the issue:
https://github.com/apache/nifi/pull/2866
To echo what @bbende said, SPNEGO is far preferred over the form field for
Kerberos username and password, that feature was provided solely as a fallback
system for legacy browsers that did not support GSS-API SSO, and there have
been requests to remove or disable that functionality completely. This addition
should support the SPNEGO feature as a first class feature. ---
