Creating a proxy to another web api with Asp.net core

Question

I\'m developing an ASP.Net Core web application where I need to create a kind of \"authentication proxy\" to another (external) web service.

What I mean by authentic

Answer 1

I had luck using twitchax's AspNetCore.Proxy NuGet package, but could not get it to work using the ProxyRoute method shown in twitchax's answer. (Could have easily been a mistake on my end.)

Instead I defined the mapping in Statup.cs Configure() method similar to the code below.

app.UseProxy("api/someexternalapp-proxy/{arg1}", async (args) =>
{
    string url = "https://someexternalapp.com/" + args["arg1"];
    return await Task.FromResult<string>(url);
});

Answer 2

Twitchax's answer seems to be the best solution at the moment. In researching this, I found that Microsoft is developing a more robust solution that fits the exact problem the OP was trying to solve.

Repo: https://github.com/microsoft/reverse-proxy

Article for Preview 1 (they actually just released prev 2): https://devblogs.microsoft.com/dotnet/introducing-yarp-preview-1/

From the Article...

YARP is a project to create a reverse proxy server. It started when we noticed a pattern of questions from internal teams at Microsoft who were either building a reverse proxy for their service or had been asking about APIs and technology for building one, so we decided to get them all together to work on a common solution, which has become YARP.

YARP is a reverse proxy toolkit for building fast proxy servers in .NET using the infrastructure from ASP.NET and .NET. The key differentiator for YARP is that it is being designed to be easily customized and tweaked to match the specific needs of each deployment scenario. YARP plugs into the ASP.NET pipeline for handling incoming requests, and then has its own sub-pipeline for performing the steps to proxy the requests to backend servers. Customers can add additional modules, or replace stock modules as needed.
...
YARP works with either .NET Core 3.1 or .NET 5 preview 4 (or later). Download the preview 4 (or greater) of .NET 5 SDK from https://dotnet.microsoft.com/download/dotnet/5.0

More specifically, one of their sample apps implements authentication (as for the OP's original intent) https://github.com/microsoft/reverse-proxy/blob/master/samples/ReverseProxy.Auth.Sample/Startup.cs