user: (character) username, required. see Details.
pwd: (character) password, required. see Details.
auth: (character) authentication type, one of basic (default), digest, digest_ie, gssnegotiate, ntlm, or any. required
Details
Only supporting simple auth for now, OAuth later maybe.
For user and pwd you are required to pass in some value. The value can be NULL to - which is equivalent to passing in an empty string like "" in httr::authenticate. You may want to pass in NULL for both user and pwd for example if you are using gssnegotiate auth type. See example below.