解决 asp.net core swagger nginx 代理服务器转发后，无法访问的问题 Swashbuckle

通过代理转发后，webapi的swagger无法访问，本质原因是代理后url路径发生变化导致swagger无法定位到json。

官方文档配置：
https://docs.microsoft.com/en-us/aspnet/core/tutorials/getting-started-with-swashbuckle
https://docs.microsoft.com/en-us/aspnet/core/host-and-deploy/linux-nginx?view=aspnetcore-3.1#use-a-reverse-proxy-server

Copyc.SwaggerEndpoint("/swagger/v1/swagger.json", "My API V1");

解决方法：

1. 使用url相对路径
2. 通过PreSerializeFilters设置根地址，并通过nginx的X-Forwarded-Prefix指定api名称

nginx配置：

Copyserver {
        listen       5011;
        server_name  _;

        location /api1/ {
            proxy_pass         http://192.168.56.1:5000/;
            proxy_http_version 1.1;
            proxy_set_header   Upgrade $http_upgrade;
            proxy_set_header   Connection keep-alive;
            proxy_set_header   Host $http_host; # 使用http_host而非host以满足带有端口号的情况
            proxy_cache_bypass $http_upgrade;
            proxy_set_header   X-Forwarded-For $proxy_add_x_forwarded_for;
            proxy_set_header   X-Forwarded-Proto $scheme;
	    proxy_set_header   X-Forwarded-Prefix api1; # api1用于传递路由名称
        }
    }

Swashbuckle 5.x 以前通过PreSerializeFilters设置BasePath的方案，5.x以后，设置OpenApiServer.Url属性

代码如下：

Copyapp.UseSwagger(c =>
{
	c.PreSerializeFilters.Add((swagger, httpReq) =>
	{
                //根据访问地址，设置swagger服务路径
		swagger.Servers = new List<OpenApiServer> { new OpenApiServer { Url = $"{httpReq.Scheme}://{httpReq.Host.Value}/{httpReq.Headers["X-Forwarded-Prefix"]}" } };
	});
});

app.UseSwaggerUI(c =>
{
        //使用相对路径
	c.SwaggerEndpoint("v1/swagger.json", "My API V1");
});

github demo： https://github.com/wswind/swagger-proxy

相关issue:

https://github.com/domaindrivendev/Swashbuckle.AspNetCore/issues/1617
https://github.com/microsoft/service-fabric-issues/issues/327
https://github.com/domaindrivendev/Swashbuckle.AspNetCore/issues/662
https://github.com/domaindrivendev/Swashbuckle.AspNetCore/issues/427
https://github.com/domaindrivendev/Swashbuckle.AspNetCore/issues/380
https://github.com/domaindrivendev/Swashbuckle.AspNetCore/issues/1298#issuecomment-620269062
https://github.com/domaindrivendev/Swashbuckle.AspNetCore/issues/1253