Remove secondary middleware caching

[andrew-laughlin]

• There were 2 caching mechanisms in play. One in this middleware and one in the ConfigurationManager dependency. This change removes the caching the middleware and delegates it the ConfigurationManager.

• Exposes the cache provider's refresh time via options. This allows the middleware's metadata refresh time to be configurable. The default refresh time is 1 day.

See issue: #https://github.com/IdentityServer/IdentityServer3.AccessTokenValidation/issues/143

[dnfclas]

@andrew-laughlin, Thanks for your contribution. To ensure that the project team has proper rights to use your work, please complete the Contribution License Agreement at https://cla2.dotnetfoundation.org.

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[brockallen]

Thanks Andrew -- a few asks: 1) Can you sign the CLA, please?, and 2) Can you rework the PR to only make the code changes, and not the dependency updates?

Thanks.

[dnfclas]

@andrew-laughlin, thanks for signing the contribution license agreement. We will now validate the agreement and then the pull request.
Thanks, .NET Foundation Pull Request Bot

[andrew-laughlin]

@brockallen updates made, please take a look.

[brockallen]

great, thanks!

[leastprivilege]

nuget pushed

[ErikEJ]

It looks like this change causes thread deadlocks/hangs under heavy load (many request running under ASP.NET) - why was the quick exit removed? https://github.com/IdentityServer/IdentityServer3.AccessTokenValidation/commit/dec7f5c14784ddcaeb3c99aaf3cced7ddf22eed1#diff-5b2c5cc8b17ae721dd148a69c90508e6L136