Startup.cs - The path in 'value' must star

Question

I have created a new .NET Core MVC application in Visual Studio 2017 and enabled multi-tenant authentication.
I've completed the configuration (ClientId, Authority, etc) but when I debug the application there is an exception in the Startup.cs, specifically the app.useOpenIdConnectAuthentication method.

The exception given is

System.ArgumentException: The path in 'value' must start with '/'.

I'm a bit of a novice when it comes to C# and .NET Core, so I'm not sure whether I'm missing something obvious. The main sticking point is what the debugger is referring to with the parameter 'value' as I can't see any mention of it in the code. There are no changes beyond the default template generated by visual studio, other than adding the configuration items to the appsettings.json.

Answer 1

As there is no code in the question, so I will try to make general answer as possible.
The previous exception appears when you use this overload PathString.FromUriComponent(string) and the string does not start with the / character

so,for example, the following code will throw an exception :

PathString.FromUriComponent("controllerName/actionName"); // throw exception

and to fix the previous exception you can write it like this

PathString.FromUriComponent("/controllerName/actionName"); 

and of course, this will be a relative path.

In case you wanted to write an absolute path, (and not start your string with /), then you must use another overload of this method which takes Uri instead of string

here is an example

PathString.FromUriComponent(new Uri("https://localhost:8000/controller/action/"))

Answer 2

I also had a similar issue:

The error was:

ArgumentException: The path in 'value' must start with '/'. Nombre del parámetro: value Microsoft.AspNetCore.Http.PathString..ctor(string value) Microsoft.AspNetCore.Builder.ExceptionHandlerExtensions.UseExceptionHandler(IApplicationBuilder app, string errorHandlingPath)

Fixed by replacing

  app.UseExceptionHandler("Home/Error");

with

  app.UseExceptionHandler("/Home/Error");

Also you can try deploying with

  app.UseDeveloperExceptionPage();

and find the error if any.