Attempting to retrieve a session token via POST method using apoc.load.jsonParams

I am attempting to use apoc.load.jsonParams to query a Veeam backup web API.
[https://helpcenter.veeam.com/docs/backup/rest/http_authentication.html?ver=95u4](http://Veeam API documentation)

I've done this using APOC with several other APIs, and typically it's something like this

WITH "http://myapiserverurl:9399/api/sessionMngr/?v=latest" as url,"mybase64encodedcredentials" as token
CALL apoc.load.jsonParams(url,{Authorization:" Basic "+token,Accept:"application/json"}) yield value
RETURN value

and away I go.
However I kept getting a 401 (unauthorized) error.
Reading their documentation it says I must perform a POST to get the session token, so I tried that:

WITH "http://myapiserverurl:9399/api/sessionMngr/?v=latest" as url,"mybase64encodedcredentials" as token
CALL apoc.load.jsonParams(url,{Authorization:" Basic "+token,method:"POST"},null) yield value
RETURN value

This results in an error:
Neo.ClientError.Procedure.ProcedureCallFailed: Failed to invoke procedure apoc.load.jsonParams: Caused by: java.lang.RuntimeException: Can't read url or key http://myapiserverurl:9399/api/sessionMngr/?v=latest as json: cannot write to a URLConnection if doOutput=false - call setDoOutput(true)

The POST method of apoc.load.json Params requires a "Query" instead of the null entry. But I'm not actually wanting to query anything, I just want to POST to this URL with the authorization header, so I can get my session token back to use to query the system.

Any ideas here?

Further investigation reveals that in addition to the "POST" method, the session token I need to further query is not in the JSON response, but within the HTTP header data. I don't think the APOC functions have a method to retrieve HTTP header data do they?

It's looking like I'm going to be stuck performing this with 2 methods.. powershell to query for the session token, then inject (find/replace) the session ID and validation token into the cypher code and use the apoc.load.json to collect data after that.

Anyone have any other ideas?