hotfix(voice, auth): handle zero byte array in app signature

src/Sinch/Auth/ApplicationSignedAuth.cs

@@ -38,7 +38,7 @@ public string GetSignedAuth(byte[] jsonBodyBytes, string httpVerb,
         public Task<string> GetAuthToken(bool force = false)
         {
             var encodedBody = string.Empty;
-            if (_jsonBodyInBytes is not null)
+            if (_jsonBodyInBytes is not null && _jsonBodyInBytes.Length > 0)
             {
                 var md5Bytes = MD5.HashData(_jsonBodyInBytes);
                 encodedBody = Convert.ToBase64String(md5Bytes);

src/Sinch/SinchClient.cs

@@ -120,7 +120,11 @@ public class SinchClient : ISinchClient
         private const string SmsApiUrlTemplate = "https://zt.{0}.sms.api.sinch.com";
         private const string SmsApiServicePlanIdUrlTemplate = "https://{0}.sms.api.sinch.com";
         private const string ConversationApiUrlTemplate = "https://{0}.conversation.api.sinch.com/";
+
         private const string VoiceApiUrlTemplate = "https://{0}.api.sinch.com/";
+
+        // apparently, management api for applications have a different set url
+        private const string VoiceApiApplicationManagementUrl = "https://callingapi.sinch.com/";
         private const string AuthApiUrl = "https://auth.sinch.com";
         private const string TemplatesApiUrlTemplate = "https://{0}.template.api.sinch.com/";
 
@@ -281,7 +285,8 @@ public ISinchVoiceClient Voice(string appKey, string appSecret,
             var http = new Http(auth, _httpClient, _loggerFactory?.Create<IHttp>(), JsonNamingPolicy.CamelCase);
             return new SinchVoiceClient(
                 new Uri(_apiUrlOverrides?.VoiceUrl ?? string.Format(VoiceApiUrlTemplate, voiceRegion.Value)),
-                _loggerFactory, http, (auth as ApplicationSignedAuth)!);
+                _loggerFactory, http, (auth as ApplicationSignedAuth)!,
+                new Uri(_apiUrlOverrides?.VoiceUrl ?? VoiceApiApplicationManagementUrl));
         }
 
         private void ValidateCommonCredentials()

src/Sinch/Voice/SinchVoiceClient.cs

@@ -57,14 +57,15 @@ internal class SinchVoiceClient : ISinchVoiceClient
         private readonly ILoggerAdapter<ISinchVoiceClient>? _logger;
 
         public SinchVoiceClient(Uri baseAddress, LoggerFactory? loggerFactory,
-            IHttp http, ApplicationSignedAuth applicationSignedAuth)
+            IHttp http, ApplicationSignedAuth applicationSignedAuth, Uri applicationManagementBaseAddress)
         {
             _applicationSignedAuth = applicationSignedAuth;
             _logger = loggerFactory?.Create<ISinchVoiceClient>();
             Callouts = new SinchCallout(loggerFactory?.Create<ISinchVoiceCallout>(), baseAddress, http);
             Calls = new SinchCalls(loggerFactory?.Create<ISinchVoiceCalls>(), baseAddress, http);
             Conferences = new SinchConferences(loggerFactory?.Create<ISinchVoiceConferences>(), baseAddress, http);
-            Applications = new SinchApplications(loggerFactory?.Create<ISinchVoiceApplications>(), baseAddress, http);
+            Applications = new SinchApplications(loggerFactory?.Create<ISinchVoiceApplications>(),
+                applicationManagementBaseAddress, http);
         }
 
         /// <inheritdoc />

tests/Sinch.Tests/AuthTests.cs

@@ -128,12 +128,14 @@ public void GenerateCorrectApplicationSignature()
                 .BeEquivalentTo("669E367E-6BBA-48AB-AF15-266871C28135:h6rXrFayOoggyHW4ymnLlfSDkZZPg6j98lHzvOXVjvw=");
         }
 
-        [Fact]
-        public void AppSignatureWithEmptyBody()
+        [Theory]
+        [InlineData(new byte[0])]
+        [InlineData(null)]
+        public void AppSignatureWithEmptyBody(byte[] data)
         {
             var auth = new ApplicationSignedAuth("669E367E-6BBA-48AB-AF15-266871C28135", "BeIukql3pTKJ8RGL5zo0DA==");
 
-            var result = auth.GetSignedAuth(null, "POST", "/verification/v1/verifications",
+            var result = auth.GetSignedAuth(data, "POST", "/verification/v1/verifications",
                 "x-timestamp:2014-06-04T13:41:58Z",
                 "application/json");