Coinbase API invalid signature with Powershell - api

Question

I would like to retrieve account balance through Coinbase API with Powershell.
I coded the following reading from coinbase api documentation but the last request throws the following error:
Invoke-RestMethod : {"errors":[{"id":"authentication_error","message":"invalid signature"}]}
Here is my code.
What's wrong? Thank you.
$accounts = 'https://api.coinbase.com/v2/accounts'
$time = 'https://api.coinbase.com/v2/time'
$epochtime = [string]((Invoke-WebRequest $time | ConvertFrom-Json).data).epoch
$method = 'GET'
$requestpath = '/v2/accounts'
$secret_key = 'xxxxxxxxxxxxxxxxxxxxxxxxxxxxx'
$sign = $epochtime + $method + $requestpath
$hmacsha = New-Object System.Security.Cryptography.HMACSHA256
$hmacsha.key = [Convert]::FromBase64String($secret_key)
$signature = $hmacsha.ComputeHash([Text.Encoding]::ASCII.GetBytes($sign))
$signature = [Convert]::ToBase64String($signature)
$header = #{
"CB-ACCESS-SIGN"=$signature
"CB-ACCESS-TIMESTAMP"=$epochtime
"CB-VERSION" = '2017-08-07'
"CB-ACCESS-KEY"='xxxxxxxxxxxxxx'
}
Invoke-WebRequest $accounts -Headers $header

Answer 1

Hopefully this will get you going. I just started working on a module today and got stuck on the same thing. I came across your question while trying to solve the problem myself. Figured I would share what I found. Good luck!
$accounts = 'https://api.coinbase.com/v2/accounts'
$time = 'https://api.coinbase.com/v2/time'
$epochtime = [string]((Invoke-WebRequest $time | ConvertFrom-Json).data).epoch
$method = 'GET'
$requestpath = '/v2/accounts'
$secret_key = (Get-CoinBaseAPIKeys).Secret
$sign = $epochtime + $method + $requestpath
$hmacsha = New-Object System.Security.Cryptography.HMACSHA256
$hmacsha.key = [Text.Encoding]::UTF8.GetBytes($secret_key)
$computeSha = $hmacsha.ComputeHash([Text.Encoding]::UTF8.GetBytes($sign))
The LONG WAY, for reference:
$signature = ""
foreach ( $c in $computeSha )
{
$signature += "{0:x2}" -f $c
}
The short way. Oddly I got stuck on this SAME issue, because the short way
produces UPPER CASE HEX and the long way ^^above^^ converts to lower case HEX.
The CoinBase API will ONLY accept the signature in HEX in lower case.
$signature = ([System.BitConverter]::ToString($computeSha) -replace "-").ToLower()
Now that we have the signature figured out, the rest should work great. I removed the CB_VERSION because it will default to your OWN API version. My default was different, so I simply removed it.
$header = #{
"CB-ACCESS-SIGN"=$signature
"CB-ACCESS-TIMESTAMP"=$epochtime
"CB-ACCESS-KEY"=(Get-CoinBaseAPIKeys).Key
}
$result = Invoke-WebRequest $accounts -Headers $header -Method Get -ContentType "application/json"
$accounts = $result.Content | ConvertFrom-Json
Write-Output $accounts.data
As an aside on storing PRIVATE KEY/SECRET you can find some ideas here:
https://github.com/cmaahs/BittrexAPI/tree/master/Encryption. Feel free to grab it and modify as you will. Better to store your KEY/SECRET encrypted in the registry rather than as plain text in your script or as environment variables.