Extract loading and saving certificates; certificate caching improvements

[antrv]

Hi!

I need the ability to have my own certificate disk cache, so I did the following:

• abstracted loading and saving certificates through interface ICertificateCache
• extracted loading and saving certificates into separate class DefaultCertificateDiskCache with the same behavior as before
• added Cache property into CertificateManager class
• by default CertificateManager uses DefaultCertificateDiskCache class as a ICertificateCache implementation

Also I did some certificate caching improvements:

• certificate creation tasks moved from separate ConcurrentDictionary to CachedCertificate class
• ClearIdleCertificates method now uses CancellationToken to stop the loop
• added lock into the CreateRootCertificate method to prevent parallel creation of several root certificates

Doneness:

• Build is okay - I made sure that this change is building successfully.
• No Bugs - I made sure that this change is working properly as expected. It doesn't have any bugs that you are aware of.
• Branching - If this is not a hotfix, I am making this request against master branch

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❌ Build Titanium-Web-Proxy 3.0.732 failed (commit 4bbb42366c by @)

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✅ Build Titanium-Web-Proxy 3.0.733 completed (commit bfbd97e736 by @)

[justcoding121]

Why are we setting the Task to null.

[antrv]

This is the task that creates a certificate. The task assigns Certificate property to the generated certificate and cleans CreationTask property to allow the Task memory to be released by GC.

[justcoding121]

Shouldn't this be just item!=null ?

[antrv]

item is always not null.
Actually this condition checks if the certificate creation task is completed, If the certificate creation task is not completed then the Certificate property of the item is null.

[justcoding121]

Okay. I refactored it removing locking while also preventing multiple tasks for same certificate.