Allows restriction of cors requests when using the app.UseCors() rather than just CorsOptions.AllowAll

CorsOptionsExt.cs

/// <summary>
/// To be used with CorsMiddleware <code>app.UseCors()</code> where origins are restricted to the parameters passed in.
/// </summary>
public partial class CorsOptionsExt { 

	public static CorsOptions AllowOrigins(params string[] origins) {

		return new CorsOptions() {

			PolicyProvider = new CorsPolicyProvider() {

				PolicyResolver = (context) => {

					var policy = new CorsPolicy() {
						AllowAnyHeader = true,
						AllowAnyMethod = true,
						SupportsCredentials = true,
					};

					foreach (var item in origins) {
						policy.Origins.Add(item);
					}

					return Task.FromResult(policy);
				}
			}
		};
	}
}

Usage:

app.UseCors(CorsOptionsExt.AllowOrigins("http://localhost:8080", "http://localhost:8000"));