Support Kerberos Credentials based Basic Authentication

[guruchai]

Currently, we have to authentication handlers

1. Kerberos SPNEGO Authentication Handler
2. Knox based JWT handler.

We are introducing a new authentication handler(KerberosLoginAuthenticationHandler) which allows to authenticate a user based on userId and password he/she provides in https POST request. In the absence of credentials or https or login failure, SPNEGO is attempted just as it's done now.
The handler expects the credentials in the Authorization header of the request in Base64 encoded bytes of "userId:password" string.