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HTTPS connection failed in Composer

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Lex asked on 19 May 2020, 04:23 AM

Found an issue when testing HTTPS connection with Composer on macOS.

I used the following steps,

1. Install .NET Core SDK.

2. Run "dotnet new mvc" to create an ASP.NET Core project.

3. Run "dotnet dev-certs https" to configure default development certificate.

4. Run "dotnet run" to launch this project at http://localhost:5000 and https://localhost:5001.

Note that https://localhost:5001 can now be opened in Safari without any problem, as step 3 allows Safari to trust the certificate.

Open Fiddler Composer and try to do the same. The error happens,


HTTP/1.1 502 Fiddler - Connection Failed
Date: Tue, 19 May 2020 04:19:37 GMT
Content-Type: text/html; charset=UTF-8
Connection: close
Cache-Control: no-cache, must-revalidate
Timestamp: 00:19:37.347


Raw tab shows an exception,


[Fiddler] The connection to 'localhost' failed.  <br />System.Security.SecurityException Failed to negotiate HTTPS connection with; HTTPS handshake to localhost (for #13) failed. System.IO.IOException Authentication failed because the remote party has closed the transport stream.


This also triggers an exception recorded on ASP.NET Core side,


dbug: HttpsConnectionAdapter[1]
      Failed to authenticate HTTPS connection.
System.Security.Authentication.AuthenticationException: Authentication failed, see inner exception. ---> Interop+AppleCrypto+SslException: Cipher Suite negotiation failure
   --- End of inner exception stack trace ---
   at System.Net.Security.SslState.StartSendAuthResetSignal(ProtocolToken message, AsyncProtocolRequest asyncRequest, ExceptionDispatchInfo exception)
   at System.Net.Security.SslState.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.StartSendBlob(Byte[] incoming, Int32 count, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.ProcessReceivedBlob(Byte[] buffer, Int32 count, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.StartReadFrame(Byte[] buffer, Int32 readBytes, AsyncProtocolRequest asyncRequest)
   at System.Net.Security.SslState.PartialFrameCallback(AsyncProtocolRequest asyncRequest)
--- End of stack trace from previous location where exception was thrown ---
   at System.Net.Security.SslState.ThrowIfExceptional()
   at System.Net.Security.SslState.InternalEndProcessAuthentication(LazyAsyncResult lazyResult)
   at System.Net.Security.SslState.EndProcessAuthentication(IAsyncResult result)
   at System.Net.Security.SslStream.EndAuthenticateAsServer(IAsyncResult asyncResult)
   at System.Net.Security.SslStream.<>c.<AuthenticateAsServerAsync>b__51_1(IAsyncResult iar)
   at System.Threading.Tasks.TaskFactory`1.FromAsyncCoreLogic(IAsyncResult iar, Func`2 endFunction, Action`1 endAction, Task`1 promise, Boolean requiresSynchronization)
--- End of stack trace from previous location where exception was thrown ---
   at Microsoft.AspNetCore.Server.Kestrel.Https.Internal.HttpsConnectionAdapter.InnerOnConnectionAsync(ConnectionAdapterContext context)


Not quite sure why HTTPS connection failed in this way, but hope it can be investigated and resolved.

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Nick Iliev
Telerik team
answered on 19 May 2020, 07:40 AM

Hello Lex Li,


Thank you for using Fiddler Everywhere and for being a valued customer.

There are some specific when using Fiddler with .Net applications. Note that as stated in this documentation article .NET will always try to bypass the Fiddler proxy. Try the provided solution (which is for the classic Fiddler but should also work as expected for Fiddler Everywhere).


Nick Iliev
Progress Telerik

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