ASP.NET Core 7中出站POST请求被转为GET的原因是什么？

我有两个部署在Azure App Service上的ASP.NET Core 7应用，特定场景下service1需要通过私有VNet向service2发送POST请求。该请求在预发布（staging）环境运行正常，但生产环境中POST请求被转为GET请求，导致调用失败。

请问.NET Core中出站POST请求被转为GET请求的可能原因有哪些？

上下文信息：为Refit添加额外日志 #

Refit客户端配置代码 #

services
    .AddRefitClient<IService2Api>(
        (sp) =>
            new RefitSettings
            {
                CollectionFormat = CollectionFormat.Multi,
                HttpMessageHandlerFactory = () =>
                    new LoggingHandler(
                        sp.GetRequiredService<ILoggerFactory>()
                            .CreateLogger<LoggingHandler>(),
                        new HttpClientHandler() { AllowAutoRedirect = true }
                    )
            }
    )
    .ConfigureHttpClient(
        // ...

LoggingHandler实现代码 #

private class LoggingHandler : DelegatingHandler
{
    private readonly ILogger<LoggingHandler> logger;

    public LoggingHandler(ILogger<LoggingHandler> logger, HttpMessageHandler innerHandler)
        : base(innerHandler)
    {
        this.logger = logger;
    }

    protected override HttpResponseMessage Send(
        HttpRequestMessage request,
        CancellationToken cancellationToken
    )
    {
        logger.LogDebug("Before [{Method}] to {Url}", request.Method, request.RequestUri);
        var response = base.Send(request, cancellationToken);
        logger.LogDebug("After [{Method}] to {Url}", request.Method, request.RequestUri);
        return response;
    }

    protected override async Task<HttpResponseMessage> SendAsync(
        HttpRequestMessage request,
        CancellationToken cancellationToken
    )
    {
        logger.LogDebug("Before [{Method}] to {Url}", request.Method, request.RequestUri);
        var response = await base.SendAsync(request, cancellationToken);
        logger.LogDebug("After [{Method}] to {Url}", request.Method, request.RequestUri);
        return response;
    }
}

日志内容 #

2023-11-24 23:34:11.315 +00:00 [Information] System.Net.Http.HttpClient.Refit.Implementation.Generated+IService2Api, Common, Version=1.0.1.0, Culture=neutral, PublicKeyToken=null.ClientHandler: Sending HTTP request POST http://service2.azurewebsites.net/my/endpoint/
2023-11-24 23:34:11.315 +00:00 [Trace] System.Net.Http.HttpClient.Refit.Implementation.Generated+IService2Api, Common, Version=1.0.1.0, Culture=neutral, PublicKeyToken=null.ClientHandler: Request Headers:
Authorization: Bearer [Redacted]
User-Agent: Service1, (Service1/1.0.1.0)
Content-Type: application/json; charset=utf-8

2023-11-24 23:34:11.315 +00:00 [Debug] LoggingHandler: Before [POST] to http://service2.azurewebsites.net/my/endpoint/
2023-11-24 23:34:11.400 +00:00 [Debug] LoggingHandler: After [GET] to https://service2.azurewebsites.net/my/endpoint/
2023-11-24 23:34:11.401 +00:00 [Information] System.Net.Http.HttpClient.Refit.Implementation.Generated+IService2Api, Common, Version=1.0.1.0, Culture=neutral, PublicKeyToken=null.ClientHandler: Received HTTP response headers after 85.2956ms - 405
2023-11-24 23:34:11.401 +00:00 [Trace] System.Net.Http.HttpClient.Refit.Implementation.Generated+IService2Api, Common, Version=1.0.1.0, Culture=neutral, PublicKeyToken=null.ClientHandler: Response Headers:
Date: Fri, 24 Nov 2023 23:34:11 GMT
Set-Cookie: [Redacted]
Content-Length: 0
Allow: POST

可能的原因分析 #

从日志可见，请求原本使用http协议发送POST，最终被重定向到https协议并转为GET，结合环境和.NET HttpClient行为，核心原因如下：

• HttpClient自动重定向的默认行为：
  HttpClientHandler的AllowAutoRedirect默认开启，当服务器返回301/302重定向时，HttpClient会遵循早期HTTP规范，将原始POST请求转为GET请求跟进重定向。

• Azure App Service强制HTTPS配置差异：
  生产环境的Azure App Service大概率开启了强制HTTPS设置（预发布环境未开启），当收到HTTP请求时会返回301/302重定向到HTTPS地址，触发了上述HttpClient的重定向行为。

• 未明确配置重定向策略：
  当前代码中HttpClientHandler仅设置了AllowAutoRedirect = true，未指定重定向时保留请求方法的策略，导致默认行为生效。

解决建议 #

1. 直接使用HTTPS地址调用：将请求目标改为https://service2.azurewebsites.net，从根源避免重定向触发。
2. 修改HttpClient重定向配置：
   • 关闭自动重定向（AllowAutoRedirect = false），手动处理重定向逻辑；
   • 若需保留自动重定向，使用SocketsHttpHandler并配置RedirectPolicy，确保重定向时保留POST方法（.NET Core 2.1+支持）。
3. 检查Azure环境配置：确认生产环境App Service的强制HTTPS设置，根据业务需求调整或确保请求全程使用HTTPS。

内容的提问来源于stack exchange，提问作者Felix ZY