make C# interop test args parsing compliant with spec

src/csharp/Grpc.IntegrationTesting/InteropClient.cs

@@ -66,11 +66,13 @@ namespace Grpc.IntegrationTesting
             [Option("test_case", DefaultValue = "large_unary")]
             public string TestCase { get; set; }
 
-            [Option("use_tls")]
+            // Deliberately using nullable bool type to allow --use_tls=true syntax (as opposed to --use_tls)
-            public bool UseTls { get; set; }
+            [Option("use_tls", DefaultValue = false)]
+            public bool? UseTls { get; set; }
 
-            [Option("use_test_ca")]
+            // Deliberately using nullable bool type to allow --use_test_ca=true syntax (as opposed to --use_test_ca)
-            public bool UseTestCa { get; set; }
+            [Option("use_test_ca", DefaultValue = false)]
+            public bool? UseTestCa { get; set; }
 
             [Option("default_service_account", Required = false)]
             public string DefaultServiceAccount { get; set; }
@@ -134,7 +136,7 @@ namespace Grpc.IntegrationTesting
 
         private async Task<ChannelCredentials> CreateCredentialsAsync()
         {
-            var credentials = options.UseTls ? TestCredentials.CreateTestClientCredentials(options.UseTestCa) : ChannelCredentials.Insecure;
+            var credentials = options.UseTls.Value ? TestCredentials.CreateTestClientCredentials(options.UseTestCa.Value) : ChannelCredentials.Insecure;
 
             if (options.TestCase == "jwt_token_creds")
             {

src/csharp/Grpc.IntegrationTesting/InteropServer.cs

@@ -54,8 +54,9 @@ namespace Grpc.IntegrationTesting
             [Option("port", DefaultValue = 8070)]
             public int Port { get; set; }
 
-            [Option("use_tls")]
+            // Deliberately using nullable bool type to allow --use_tls=true syntax (as opposed to --use_tls)
-            public bool UseTls { get; set; }
+            [Option("use_tls", DefaultValue = false)]
+            public bool? UseTls { get; set; }
 
             [HelpOption]
             public string GetUsage()
@@ -99,7 +100,7 @@ namespace Grpc.IntegrationTesting
 
             string host = "0.0.0.0";
             int port = options.Port;
-            if (options.UseTls)
+            if (options.UseTls.Value)
             {
                 server.Ports.Add(host, port, TestCredentials.CreateTestServerCredentials());
             }

tools/run_tests/run_interop_tests.py

@@ -100,17 +100,17 @@ class CSharpLanguage:
 
   def cloud_to_prod_args(self):
     return (self.client_cmdline_base + _CLOUD_TO_PROD_BASE_ARGS +
-            ['--use_tls'])
+            ['--use_tls=true'])
 
   def cloud_to_cloud_args(self):
     return (self.client_cmdline_base + _CLOUD_TO_CLOUD_BASE_ARGS +
-            ['--use_tls', '--use_test_ca'])
+            ['--use_tls=true', '--use_test_ca=true'])
 
   def cloud_to_prod_env(self):
     return _SSL_CERT_ENV
 
   def server_args(self):
-    return ['mono', 'Grpc.IntegrationTesting.Server.exe', '--use_tls']
+    return ['mono', 'Grpc.IntegrationTesting.Server.exe', '--use_tls=true']
 
   def __str__(self):
     return 'csharp'