React+ASP.NET.Core : No 'Access-Control-Allow-Origin' header is present on the requested resource

Question

Actually this is not a duplication post,I know a part of the title asked many times in stackoverflow community, I read all posts, and answers, but I think m

Answer 1

With ASP.NET Core 2.1, when the controller throws an exception, which results in an error 500, the CORS headers are not sent. This should be fixed in the next version but until then you could use a middleware to fix this.

see

• https://github.com/aspnet/CORS/issues/90#issuecomment-348323102
• https://github.com/aspnet/AspNetCore/issues/2378
• https://github.com/aspnet/CORS/issues/46

Also note that with credentials you need to explicitly add WithOrigins with host and port since most browsers simply ignore it otherwise (see https://stackoverflow.com/a/19744754/2477619):

  app.UseCors(builder =>
    builder
      .WithOrigins("http://localhost:4200")
      .AllowAnyHeader()
      .AllowAnyMethod()
      .AllowCredentials()
  );