Invoke-WebRequest -Uri ("https://contoso.com/rest/api/content/123789") -Method Get -Headers $Credentials -ContentType "application/json; charset=utf-8"

$r = invoke-webrequest http://foobar.com
$r.Headers

Invoke-WebRequest http://foorbar.com -outfile .test.txt
$content = get-content .test.txt -Encoding utf8 -raw

[system.Text.Encoding]::UTF8.GetString((Invoke-WebRequest "https://www.solution.com").RawContentStream.ToArray())