React 与 Asp.net 核心项目之间的通信

Question

I am getting this error when i try and connect my react project to my asp.net core 3 back end

No 'Access-Control-Allow-Origin' header is present on the requested resource

I have up this is my startup method ConfigureServices

   services.AddCors(options =>
        {
            options.AddPolicy("AllowOrigin",
                builder => builder.AllowAnyOrigin());
        });

And I have also put this is the startup config method aswell

 app.UseCors("AllowOrigin");

Answer 1

Add these:

services.AddCors(options =>
        {
            options.AddPolicy("CorsPolicy",
                builder => builder.AllowAnyOrigin()
                .AllowAnyMethod()
                .AllowAnyHeader()
                .AllowCredentials());
        });

Answer 2

It doesn't look right what you did. The name of your cors policy and cors policy you use are not same. It has to be same. Should be:

app.UseCors("AllowOrigin");

Or what ever your cors policy name.

But also allowing any origins are dangerous. It is better you specified with origin can access this api. I give an example:

readonly string MyAllowSpecificOrigins = "_myAllowSpecificOrigins";

public void ConfigureServices(IServiceCollection services)
{
    services.AddCors(options =>
    {
        options.AddPolicy(name: MyAllowSpecificOrigins,
                          builder =>
                          {
                              builder.WithOrigins("http://example.com",
                                                  "http://www.contoso.com");
                          });
    });

    // services.AddResponseCaching();
    services.AddControllers();
}

And than:

 app.UseCors(MyAllowSpecificOrigins);

More information you can find here

Answer 3

Two issues.

Once was as describe above. The second is that you have to use https instead of http.