Startup.cs - The path in 'value' must start with '/'

问题

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.

回答1:

As there is no code in the question, so I will try to make a general answer as possible.
This 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"); // working, but as relative path

and of course, this will be a relative path.

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

here is an example

// use an absolute path
PathString.FromUriComponent(new Uri("https://localhost:8000/controller/action/"))

回答2:

I also get the same exception, but with another method UseExceptionHandler:

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");

notice the addition of the / char at the beginning of the string.

来源：https://stackoverflow.com/questions/41834645/startup-cs-the-path-in-value-must-start-with