Bittrex API call with powershell fails with INVALID_SIGNATURE - rest

Question

I haven't been successful in getting a response from the Bittrex API with the following powershell code:
Function Crypto($secret, $message)
{
$hmacsha = New-Object System.Security.Cryptography.HMACSHA512(,[System.Text.Encoding]::ASCII.GetBytes($secret))
$hashmessage = $hmacsha.ComputeHash([System.Text.Encoding]::ASCII.GetBytes($message))
$signature = [Convert]::ToBase64String($hashmessage)
return $signature
}
$apiKey = "key"
$secretApiKey = "secret"
$nonce = [Math]::Round((([DateTime]::UtcNow - [DateTime]::new(1970, 1, 1, 0, 0, 0, 0, 'Utc')).TotalSeconds),0)
$uri = "https://bittrex.com/api/v1.1/account/getbalances?apikey=$apiKey&nonce=$nonce"
$signature = Crypto $secretApiKey $uri
Invoke-RestMethod -Uri $uri -Method Get -Headers #{"apisign"="$signature"}
The response is
success message result
------- ------- ------
False INVALID_SIGNATURE
Any ideas what's missing?

Answer 1

Funny enough I ran across this as I was working on the exact same thing. I have solved the problem -- after looking at enough material I figured out the resulting header needs to be the signed data in hex format without any dashes.
Code:
### Bittrex API Key Variables
$apikey = 'KEY-GOES-HERE'
$apisecret = 'SECRET-GOES-HERE'
$byte_key = [Text.Encoding]::ASCII.GetBytes($apikey)
$byte_secret = [Text.Encoding]::ASCII.GetBytes($apisecret)
### Build the URL String
$d1 = ("01/01/1970" -as [DateTime])
[int]$int_nonce = ((New-TimeSpan -Start $d1 -End ([DateTime]::UtcNow)).TotalSeconds -as [string])
[string]$nonce = ($int_nonce -as [string])
$url = "https://bittrex.com/api/v1.1/account/getbalances?apikey=$($apikey)&nonce=$($nonce)"
$utf8enc = New-Object System.Text.UTF8Encoding
$url_bytes = $utf8enc.GetBytes($url)
### SHA 512 HASH TO HEX
$sha512 = New-Object System.Security.Cryptography.HMACSHA512
$sha512.key = $byte_secret
$sha_data = $sha512.ComputeHash($url_bytes)
$sha_sig = [System.BitConverter]::ToString($sha_data) -replace "-";
### Add Headers
$headers = New-Object "System.Collections.Generic.Dictionary[[String],[String]]"
$headers.Add("apisign",$sha_sig)
### Make the Request
$request = Invoke-WebRequest $url -Headers $headers | ConvertFrom-Json