Set up CORS in ASP.NET Core on all controllers/methods.

Startup.cs

// NuGet Microsoft.AspNet.Cors (5.2.7)
public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddCors(options => 
            options.AddDefaultPolicy(builder => 
                builder
                    .AllowAnyOrigin() // .WithOrigins(...) if .AllowCredentials
                    .AllowAnyMethod()
                    .AllowAnyHeader()
                    .AllowCredentials()));
    }
    
    public void Configure(IApplicationBuilder app, IHostingEnvironment env)
    {
        app.UseCors(); // Order is important, look into docs.
    }
}