1.HttpContext

后端：

app.UseHttpLogging();
app.MapPost("/Test", (HttpContext httpContext) =>
{
    string para = httpContext.Request.Form["para"];
    return httpContext.Response.WriteAsync($"para={para}");
});

前端：

wx.request({
    url: 'http://localhost:5140/test',
    method: 'POST',
    header: { "Content-Type": "application/x-www-form-urlencoded" },
    data: { para: "today is Tuesday" },
    success: res => console.log(res.data)
});

header: { "Content-Type": "application/x-www-form-urlencoded" }为必须项。

结果：

para=today is Tuesday