Create Custom Authentication Plugin with .NET

Last updated: 9 minutes read.

This tutorial will guide you through the creation of a custom authentication plugin for Tyk with a gRPC based plugin with .NET and C#. For additional information check the official gRPC documentation.

The sample code that we’ll use implements a very simple authentication layer using .NET and the proper gRPC bindings generated from our Protocol Buffers definition files.

Using gRPC for plugins


Create the Plugin

Create .NET Project

We use the .NET CLI tool to generate the initial files for our project:

cd ~
dotnet new console -o tyk-plugin

We now have a tyk-plugin directory containing the basic skeleton of a .NET application.

From the tyk-plugin directory we need to install a few packages that the gRPC server requires:

dotnet add package Grpc --version 1.6.0
dotnet add package System.Threading.ThreadPool --version 4.3.0
dotnet add package Google.Protobuf --version 3.4.0
  • The Grpc package provides base code for our server implementation.
  • The ThreadPool package is used by Grpc.
  • The Protobuf package will be used by our gRPC bindings.

Install the gRPC Tools

We need to install the gRPC tools to generate the bindings. We recommended you follow the official guide here:

Run the following Commands (both MacOS and Linux):

cd ~/tyk-plugin
mkdir -p $temp_dir && cd $temp_dir && curl -sL $curl_url >; unzip && cd .. && cp -r tmp/tools . && rm -rf tmp && cd ../..
chmod -Rf +x packages/Grpc.Tools.1.6.x/tools/

Then run the following, depending on your OS:

MacOS (x64)

export GRPC_TOOLS=packages/Grpc.Tools.1.6.x/tools/macosx_x64

Linux (x64)

export GRPC_TOOLS=packages/Grpc.Tools.1.6.x/tools/linux_x64

The GRPC_TOOLS environment variable will point to the appropriate GrpcTools path that matches our operating system and architecture. The last step is to export a variable for the protoc program; this is the main program used to generate bindings:


Now that we can safely run protoc, we can download the Tyk Protocol Buffers definition files. These files contain the data structures used by Tyk. See Data Structures for more information:

cd ~/tyk-plugin
git clone

Generate the bindings

To generate the bindings, we create an empty directory and run the protoc tool using the environment variable that was set before:

mkdir Coprocess
$GRPC_PROTOC -I=tyk/coprocess/proto --csharp_out=Coprocess --grpc_out=Coprocess --plugin=protoc-gen-grpc=$GRPC_TOOLS/grpc_csharp_plugin tyk/coprocess/proto/*.proto

Run the following command to check the binding directory:

ls Coprocess

The output will look like this:

CoprocessCommon.cs      CoprocessObject.cs      CoprocessReturnOverrides.cs
CoprocessMiniRequestObject.cs   CoprocessObjectGrpc.cs              CoprocessSessionState.cs

Implement Server

Create a file called Server.cs.

Add the following code to Server.cs.

using System;
using System.Threading.Tasks;
using Grpc.Core;

using Coprocess;

class DispatcherImpl : Dispatcher.DispatcherBase
  public DispatcherImpl()
    Console.WriteLine("Instantiating DispatcherImpl");

  // The Dispatch method will be called by Tyk for every configured hook, we'll implement a very simple dispatcher here:
  public override Task<Coprocess.Object> Dispatch(Coprocess.Object thisObject, ServerCallContext context)
    // thisObject is the request object:
    Console.WriteLine("Receiving object: " + thisObject.ToString());

    // hook contains the hook name, this will be defined in our plugin bundle and the implementation will be a method in this class (DispatcherImpl), we'll look it up:
    var hook = this.GetType().GetMethod(thisObject.HookName);

    // If hook is null then a handler method for this hook isn't implemented, we'll log this anyway:
    if (hook == null)
      Console.WriteLine("Hook name: " + thisObject.HookName + " (not implemented!)");
      // We return the unmodified request object, so that Tyk can proxy this in the normal way.
      return Task.FromResult(thisObject);

    // If there's a handler method, let's log it and proceed with our dispatch work:
    Console.WriteLine("Hook name: " + thisObject.HookName + " (implemented)");

    // This will dynamically invoke our hook method, and cast the returned object to the required Protocol Buffers data structure:
    var output = hook.Invoke(this, new object[] { thisObject, context });
    return (Task<Coprocess.Object>)output;

  // MyPreMiddleware implements a PRE hook, it will be called before the request is proxied upstream and before the authentication step:
  public Task<Coprocess.Object> MyPreMiddleware(Coprocess.Object thisObject, ServerCallContext context)
    Console.WriteLine("Calling MyPreMiddleware.");
    // We'll inject a header in this request:
    thisObject.Request.SetHeaders["my-header"] = "my-value";
    return Task.FromResult(thisObject);

  // MyAuthCheck implements a custom authentication mechanism, it will initialize a session object if the token matches a certain value:
  public Task<Coprocess.Object> MyAuthCheck(Coprocess.Object thisObject, ServerCallContext context)
    // Request.Headers contains all the request headers, we retrieve the authorization token:
    var token = thisObject.Request.Headers["Authorization"];
    Console.WriteLine("Calling MyAuthCheck with token = " + token);

    // We initialize a session object if the token matches "abc123":
    if (token == "abc123")
      Console.WriteLine("Successful auth!");
      var session = new Coprocess.SessionState();
      session.Rate = 1000;
      session.Per = 10;
      session.QuotaMax = 60;
      session.QuotaRenews = 1479033599;
      session.QuotaRemaining = 0;
      session.QuotaRenewalRate = 120;
      session.Expires = 1479033599;

      session.LastUpdated = 1478033599.ToString();

      thisObject.Metadata["token"] = token;
      thisObject.Session = session;
      return Task.FromResult(thisObject);


    // If the token isn't "abc123", we return the request object in the original state, without a session object, Tyk will reject this request:
    Console.WriteLine("Rejecting auth!");
    return Task.FromResult(thisObject);

Create a file called Program.cs to instantiate our dispatcher implementation and start a gRPC server.

Add the following code to Program.cs.

using System;
using Grpc.Core;

namespace tyk_plugin
  class Program

    // Port to attach the gRPC server to:
    const int Port = 5555;

    static void Main(string[] args)
      // We initialize a  Grpc.Core.Server and attach our dispatcher implementation to it:
      Server server = new Server
          Services = { Coprocess.Dispatcher.BindService(new DispatcherImpl()) },
          Ports = { new ServerPort("localhost", Port, ServerCredentials.Insecure) }

      Console.WriteLine("gRPC server listening on " + Port);
      Console.WriteLine("Press any key to stop the server...");



To run the gRPC server use the following command from the plugin directory:

dotnet run

The gRPC server will listen on port 5555 (as defined in Program.cs). In the next steps we’ll setup the plugin bundle and modify Tyk to connect to our gRPC server.

Bundle the Plugin

We need to create a manifest file within the tyk-plugin directory. This file contains information about our plugin and how we expect it to interact with the API that will load it. This file should be named manifest.json and needs to contain the following:

  "custom_middleware": {
    "driver": "grpc",
    "auth_check": {
      "name": "MyAuthMiddleware",
      "path": "",
      "raw_body_only": false,
      "require_session": false
  • The custom_middleware block contains the middleware settings like the plugin driver we want to use (driver) and the hooks that our plugin will expose. We use the auth_check hook for this tutorial. For other hooks see here.
  • The name field references the name of the function that we implement in our plugin code - MyAuthMiddleware. This will be handled by our dispatcher gRPC method (implemented in Server.cs).
  • The path field is the path to the middleware component.
  • The raw_body_only field
  • The require_session field, if set to true gives you access to the session object. It will be supplied as a session variable to your middleware processor function

To bundle our plugin run the following command in the tyk-plugin directory. Check your tyk-cli install path first:

/opt/tyk-gateway/utils/tyk-cli bundle build -y

From Tyk v2.8 upwards you can use:

/opt/tyk-gateway/bin/tyk bundle build -y

A plugin bundle is a packaged version of the plugin. It may also contain a cryptographic signature of its contents. The -y flag tells the Tyk CLI tool to skip the signing process in order to simplify the flow of this tutorial.

For more information on the Tyk CLI tool, see here.

You should now have a file in the tyk-plugin directory.

Publish the Plugin

To publish the plugin, copy or upload to a local web server like Nginx, or Apache or storage like Amazon S3. For this tutorial we’ll assume you have a web server listening on localhost and accessible through http://localhost.

Configure Tyk

You will need to modify the Tyk global configuration file tyk.conf to use gRPC plugins. The following block should be present in this file:

"coprocess_options": {
    "enable_coprocess": true,
    "coprocess_grpc_server": "tcp://localhost:5555"
"enable_bundle_downloader": true,
"bundle_base_url": "http://localhost/bundles/",
"public_key_path": ""

tyk.conf Options

  • enable_coprocess: This enables the plugin.
  • coprocess_grpc_server: This is the URL of our gRPC server.
  • enable_bundle_downloader: This enables the bundle downloader.
  • bundle_base_url: This is a base URL that will be used to download the bundle. You should replace the bundle_base_url with the appropriate URL of the web server that’s serving your plugin bundles. For now HTTP and HTTPS are supported but we plan to add more options in the future (like pulling directly from S3 buckets).
  • public_key_path: Modify public_key_path in case you want to enforce the cryptographic check of the plugin bundle signatures. If the public_key_path isn’t set, the verification process will be skipped and unsigned plugin bundles will be loaded normally.

Configure an API Definition

There are two important parameters that we need to add or modify in the API definition. The first one is custom_middleware_bundle which must match the name of the plugin bundle file. If we keep this with the default name that the Tyk CLI tool uses, it will be

"custom_middleware_bundle": ""

Assuming the bundle_base_url is http://localhost/bundles/, Tyk will use the following URL to download our file:


The second parameter is specific to this tutorial, and should be used in combination with use_keyless to allow an API to authenticate against our plugin:

"use_keyless": false,
"enable_coprocess_auth": true

enable_coprocess_auth will instruct the Tyk gateway to authenticate this API using the associated custom authentication function that’s implemented by our plugin.

Configuration via the Tyk Dashboard

To attach the plugin to an API, from the Advanced Options tab in the API Designer enter in the Plugin Bundle ID field.

Plugin Options

We also need to modify the authentication mechanism that’s used by the API. From the Core Settings tab in the API Designer select Use Custom Authentication (Python, CoProcess, and JSVM plugins) from the Target Details - Authentication Mode drop-down list.

Advanced Options

Testing the Plugin

At this point we have our test HTTP server ready to serve the plugin bundle and the configuration with all the required parameters. The final step is to start or restart the Tyk Gateway (this may vary depending on how you set up Tyk):

service tyk-gateway start

A simple CURL request will be enough for testing our custom authentication middleware.

This request will trigger an authentication error:

curl http://localhost:8080/my-api/my-path -H 'Authorization: badtoken'

This will trigger a successful authentication. We’re using the token that’s specified in our server implementation (see line 57 in Server.cs):

curl http://localhost:8080/my-api/my-path -H 'Authorization: abc123'

We also have a GitHub repository that includes tests and authentication middleware.

What’s Next?

In this tutorial we learned how Tyk gRPC plugins work. For a production-level setup we suggest the following:

  • Configure an appropriate web server and path to serve your plugin bundles.
  • See the following GitHub repo for a gRPC based .NET plugin that incorporates authentication based on Microsoft SQL Server.