VB.NET

Imports System
Imports System.Collections.Generic
Imports System.IO
Imports System.Net
Imports System.Security.Cryptography
Imports System.Text

Class Test
    Public Shared Function Main() As Integer
        Dim auth As APIAuth = New APIAuth("key", "secret")
        Dim client As APIClient = New APIClient("https://business-sandbox.cryptopay.me", auth)
        Dim path As String = "/api/invoices"
        Dim data As String = "{""price_amount"":""0.5"",""price_currency"":""ETH"",""pay_currency"":""ETH""}"
        Dim response As String = client.DoRequest(DateTime.Now, path, data)
        Console.WriteLine(response)
        Return 0
    End Function
End Class

Class APIClient
    Private baseURL As String
    Private auth As APIAuth

    Public Sub New(ByVal url As String, ByVal apiAuth As APIAuth)
        baseURL = url
        auth = apiAuth
    End Sub

    Public Function DoRequest(ByVal date As DateTime, ByVal path As String, ByVal Optional data As String = "", ByVal Optional contentType As String = "application/json", ByVal Optional Headers As List(Of KeyValuePair(Of String, String)) = Nothing, ByVal Optional verb As String = "POST") As String
        ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12
        Dim request As HttpWebRequest = CType(WebRequest.Create(baseURL & path), HttpWebRequest)
        Dim response As HttpWebResponse
        Dim sw As StreamWriter
        Dim sr As StreamReader
        Dim dateStr As String
        Dim responseData As String
        request.Method = verb
        request.ContentType = contentType
        request.ContentLength = data.Length
        request.Date = date
        dateStr = date.ToUniversalTime().ToString("r")
        request.Headers.Add("Authorization", auth.GenerateAuthorizationHeader(verb, data, contentType, dateStr, path))
        sw = New StreamWriter(request.GetRequestStream())
        sw.Write(data)
        sw.Close()
        response = CType(request.GetResponse(), HttpWebResponse)
        sr = New StreamReader(response.GetResponseStream())
        responseData = sr.ReadToEnd()
        Return (responseData)
    End Function
End Class

Class APIAuth
    Private key As String
    Private secret As String

    Public Sub New(ByVal apikey As String, ByVal apisecret As String)
        key = apikey
        secret = apisecret
    End Sub

    Public Function GenerateAuthorizationHeader(ByVal httpVerb As String, ByVal jsonBodyStr As String, ByVal httpContentType As String, ByVal dateStr As String, ByVal relativeUrl As String) As String
        Dim signature As String = GenerateSigniture(httpVerb, jsonBodyStr, httpContentType, dateStr, relativeUrl)
        Return $"HMAC {key}:{signature}"
    End Function

    Public Function GenerateSigniture(ByVal httpVerb As String, ByVal jsonBodyStr As String, ByVal httpContentType As String, ByVal dateStr As String, ByVal relativeUrl As String) As String
        Dim jsonBodyHash As String = GetMD5Hash(jsonBodyStr)
        Dim signitureData As String = String.Join(vbLf, httpVerb, jsonBodyHash, httpContentType, dateStr, relativeUrl)
        Dim apiSecretBytes As Byte() = Encoding.UTF8.GetBytes(secret)
        Dim signitureBytes As Byte() = Encoding.UTF8.GetBytes(signitureData)
        Dim hmacsha1 = New HMACSHA1(apiSecretBytes, False)
        Dim resultBytes As Byte() = hmacsha1.ComputeHash(signitureBytes)
        Return Convert.ToBase64String(resultBytes)
    End Function

    Private Function GetMD5Hash(ByVal text As String) As String
        Dim returnvalue As StringBuilder = New StringBuilder()
        Dim cryptoSP As MD5CryptoServiceProvider = New MD5CryptoServiceProvider()
        Dim HashBytes As Byte() = Encoding.UTF8.GetBytes(text)
        HashBytes = cryptoSP.ComputeHash(HashBytes)

        For Each bte As Byte In HashBytes
            returnvalue.Append(bte.ToString("x2").ToLower())
        Next

        Return returnvalue.ToString()
    End Function
End Class