ASP.NET Core 利用中间件支持跨域请求

方法1：

在Startup的ConfigureServices()中添加services.AddCors()
在Startup的Configure()中添加app.UseCors(); 保证其在app.UseMvc();之前

app.UseCors(builder => builder
    .AllowAnyOrigin()
    .AllowAnyMethod()
    .AllowAnyHeader()
    .AllowCredentials());
app.UseMvc();

原文链接

https://stackoverflow.com/questions/44379560/how-to-enable-cors-in-asp-net-core-webapi

方法2：

1、public void Configure(IApplicationBuilder app, IHostingEnvironment env)方法里面

不要加上：app.UseCors();

2、上面方法加上：

app.UseMiddleware<CorsMiddleware>();

3、中间代码如下：

public class CorsMiddleware
{
    private readonly RequestDelegate next;

    public CorsMiddleware(RequestDelegate next)
    {
        this.next = next;
    }
    public async Task Invoke(HttpContext context)
    {
        if (context.Request.Headers.ContainsKey(CorsConstants.Origin))
        {
            context.Response.Headers.Add("Access-Control-Allow-Origin", context.Request.Headers["Origin"]);
            context.Response.Headers.Add("Access-Control-Allow-Methods", "PUT,POST,GET,DELETE,OPTIONS,HEAD,PATCH");
            context.Response.Headers.Add("Access-Control-Allow-Headers", context.Request.Headers["Access-Control-Request-Headers"]);
            context.Response.Headers.Add("Access-Control-Allow-Credentials", "true");

            if (context.Request.Method.Equals("OPTIONS"))
            {
                context.Response.StatusCode = StatusCodes.Status200OK;
                return;
            }
        }

        await next(context);
    }
}