get rid of unneeded dependency on Mono.Security

src/csharp/Grpc.Auth/GoogleCredential.cs

@@ -37,7 +37,6 @@ using System.IO;
 using System.Security.Cryptography;
 
 using Google.Apis.Auth.OAuth2;
-using Mono.Security.Cryptography;
 using Newtonsoft.Json.Linq;
 using Org.BouncyCastle.Crypto.Parameters;
 using Org.BouncyCastle.Security;
@@ -113,8 +112,7 @@ namespace Grpc.Auth
         {
             // TODO(jtattermusch): temporary code to create RSACryptoServiceProvider.
             base64PrivateKey = base64PrivateKey.Replace("-----BEGIN PRIVATE KEY-----", "").Replace("\n", "").Replace("-----END PRIVATE KEY-----", "");
-            PKCS8.PrivateKeyInfo PKI = new PKCS8.PrivateKeyInfo(Convert.FromBase64String(base64PrivateKey));
-            RsaPrivateCrtKeyParameters key = (RsaPrivateCrtKeyParameters)PrivateKeyFactory.CreateKey(PKI.GetBytes());
+            RsaPrivateCrtKeyParameters key = (RsaPrivateCrtKeyParameters)PrivateKeyFactory.CreateKey(Convert.FromBase64String(base64PrivateKey));
             RSAParameters rsaParameters = DotNetUtilities.ToRSAParameters(key);
             RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
             rsa.ImportParameters(rsaParameters);

src/csharp/Grpc.Auth/Grpc.Auth.csproj

@@ -51,9 +51,6 @@
     <Reference Include="Microsoft.Threading.Tasks.Extensions.Desktop">
       <HintPath>..\packages\Microsoft.Bcl.Async.1.0.168\lib\net40\Microsoft.Threading.Tasks.Extensions.Desktop.dll</HintPath>
     </Reference>
-    <Reference Include="Mono.Security">
-      <HintPath>..\packages\Mono.Security.3.2.3.0\lib\net45\Mono.Security.dll</HintPath>
-    </Reference>
     <Reference Include="Newtonsoft.Json, Version=6.0.0.0, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed, processorArchitecture=MSIL">
       <SpecificVersion>False</SpecificVersion>
       <HintPath>..\packages\Newtonsoft.Json.6.0.6\lib\net45\Newtonsoft.Json.dll</HintPath>

src/csharp/Grpc.Auth/packages.config

@@ -7,6 +7,5 @@
   <package id="Microsoft.Bcl.Async" version="1.0.168" targetFramework="net45" />
   <package id="Microsoft.Bcl.Build" version="1.0.14" targetFramework="net45" />
   <package id="Microsoft.Net.Http" version="2.2.28" targetFramework="net45" />
-  <package id="Mono.Security" version="3.2.3.0" targetFramework="net45" />
   <package id="Newtonsoft.Json" version="6.0.6" targetFramework="net45" />
 </packages>