Request body goes missing when application is deployed to Azure - azure-web-app-service

Question

I have a net6.0 Razor pages app that is running fine locally, but doesn't work when deployed to Azure. It seems that POST bodies are going missing.
Here's some middleware...
public async Task Invoke(HttpContext context)
{
_logger.LogInformation("BodyLogger");
if (!context.Request.Body.CanSeek)
{
context.Request.EnableBuffering();
}
if (context.Request.Method == "POST")
{
_logger.LogInformation("POST cl=" + context.Request.ContentLength.ToString());
try
{
_logger.LogInformation("BodyLogger try");
string body = "";
context.Request.Body.Position = 0;
using (var reader = new StreamReader(context.Request.Body, leaveOpen: true))
{
_logger.LogInformation("BodyLogger using");
body = await reader.ReadToEndAsync();
}
context.Request.Body.Position = 0;
_logger.LogInformation($"BODY ok (length {body?.Length ?? 0})" + (body ?? "(null)"));
}
catch (Exception e)
{
_logger.LogError("BODY error " + e.Message);
throw;
}
}
await _next.Invoke(context);
}
...and what appears in ApplicationInsights.
What's going on?!
Updage
Even more strangely: it still doesn't work if it's deployed to a different Azure Web App resource, and this middleware
app.Use(async (HttpContext context, RequestDelegate next) =>
{
if (context.Request.Path == "/post")
{
if (!context.Request.Body.CanSeek)
{
context.Request.EnableBuffering();
}
//context.Request.Body.Position = 0;
context.Request.Body.Seek(0, SeekOrigin.Begin);
string body = "";
using (var reader = new StreamReader(context.Request.Body, leaveOpen: true))
{
body = await reader.ReadToEndAsync();
}
//context.Request.Body.Position = 0;
context.Request.Body.Seek(0, SeekOrigin.Begin);
await context.Response.WriteAsJsonAsync("The body was: " + body);
return;
}
await next.Invoke(context);
});
works both as the first and the last middleware.
I've noticed that absent from the ApplicationInsights logs are the Kestrel messages
Connection id "0HMOAORGGN3ES", Request id "0HMOAORGGN3ES:00000003": started reading request body.
Connection id "0HMOAORGGN3ES", Request id "0HMOAORGGN3ES:00000003": done reading request body.

Answer 1

It turns out that in some cases my custom ITelemetryInitializer for ApplicationInsights (turned off in development) was reading the request body.