Cache the CheckSessionResult Script string

[Tornhoof]

What issue does this PR address?
Reduces the allocations in CheckSessionResult by chaching the formatted string.
The script string shows up consistently as the largest string (~11k chars, 24k bytes) in my memorydumps, because the cookieName is replaced for each CheckSessionResult again.
I don't think that the cookieName is changed that often during runtime (if at all), so I cache the formatted string in a variable with checks via double locking.

Does this PR introduce a breaking change?
No

Please check if the PR fulfills these requirements

• The commit follows our guidelines
• Unit Tests for the changes have been added (for bug fixes / features)

Other information:

[msschl]

@Tornhoof I don't think this is necessary since the IdentityServerOptions is a singleton and thus for the lifetime of the application this value will never change. See AddRequiredPlatformServices.

I would suggest replacing the cookie name on the first request and store the formatted html for all following requests in a static field.

[Tornhoof]

@msschl IdentityServerOptions has public setters for each property, so it might be a singleton from a conceptional pov, but not guarenteed from the code.

[msschl]

@Tornhoof you are totally right. Sry I missed that.

[brockallen]

@Tornhoof -- i can't tell if you saw my comments? dunno if it's a review thing in github i did wrong.

[Tornhoof]

Sorry, I can't see your comments.

[leastprivilege]

https://twitter.com/iMicknl/status/1110944134733402113

[brockallen]

ok, how's that?

[brockallen]

Ok, we'll just leave it as is then. Thanks.

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.