ASP.Net Core Web Api access-control-max-age not being sent in the response header

Question

I have the SetPreFlightMaxAge in the Startup.cs. But the chrome Inspect > Network tab doesn't show it in the Response Headers.

Startup.cs

app.UseCors(o =>
{
o.WithOrigins(allowedDomains.ToArray())
.SetPreFlightMaxAge(TimeSpan.FromMinutes(10))
.AllowAnyHeader()
.AllowAnyMethod()
.AllowCredentials()
});

Response Headers (GET method): In addition to some other headers it sends these headers. There is a max-age in the third line below, but that's not the 10 mins value set in the Startup.cs

access-control-allow-credentials: true
access-control-allow-origin: ...
set-cookie: ...
strict-transport-security: max-age=2592000
vary: Origin,Accept-Encoding

Response Headers (OPTIONS method):

access-control-allow-credentials: true
access-control-allow-headers: ...
access-control-allow-origin: ...
set-cookie: ...

Answer 1

In .NET core 3.1 try adding it in ConfigureServices

services.AddCors(o => o.AddPolicy("xyzpolicy", builder =>
            {
  
                builder.AllowAnyOrigin()
                       .AllowAnyMethod()
                       .AllowAnyHeader()
                       .SetPreflightMaxAge(TimeSpan.FromMinutes(10));
            }));

They say its caped to 2 hours for Chromium-based browsers