we should specify Uri, otherwise it will throw NRE

[dohly]

Repro steps (F#):

let am=new AuthenticationManager() let ctx=am.GetACSAppOnlyContext("https://contoso.sharepoint.com/sites/mysite", clientId, clientSecret) //.................................. let cs=ctx.GetContextSettings() let t=cs.AuthenticationManager.GetAccessToken("https://contoso.sharepoint.com/sites/mysite")